Prostate Cancer: Diagnosis and evaluation

Includes 2021 CUA Best Practice Report on PET/CT and PET/MR in Prostate Cancer

Clinical Presentation of Prostate Cancer

• Only GU malignancy diagnosed by screening
  • Kidney cancer usually detected incidentally on imaging
  • Bladder cancer usually presents with hematuria
• At the time of diagnosis§
  • ≈80% present with localized disease
  • ≈12% present with regional disease
  • 5% present with metastatic disease
    • The proportion of patients presenting with metastatic disease has decreased over time, partly due to PSA screening

Diagnosis and Evaluation

UrologySchool.com Summary

• History and Physical Exam
• Labs
  • PSA
    • A newly elevated PSA value should be repeated if no prior PSA or current value inconsistent with previous trend
• Imaging
  • MRI
• Other
  • Prostate biopsy
    • If suspicion for clinically significant prostate cancer (based on history, physical exam, PSA, and MRI) and diagnosis will influence management.

History and physical exam

• History
  1. Signs and symptoms of prostate cancer
     • Localized disease is usually asymptomatic
     • Advanced disease may be associated with signs and symptoms
       • Regional symptoms: lower urinary tract symptoms, hematuria, hematospermia, bladder outlet obstruction causing renal failure, decreased ejaculate volume, and rarely, impotence
       • Metastatic symptoms: bone pain, lethargy, anemia, weight loss, pathologic fractures, and lower extremity edema; less common are malignant retroperitoneal fibrosis, paraneoplastic syndromes, disseminated intravascular coagulation, and paralysis
  2. Risk factors for prostate cancer
  3. Eligibility for investigations/treatment
     • PMHx, FHx, Meds, All, Social, etc.
       • Will patient benefit from investigations/treatment (age, competing risk (comorbidity))?
         • Is a TRUS biopsy of benefit in a 95 year-old male with a PSA 400 ng/mL ?
       • Is the patient a candidate for treatment (contraindications to radiotherapy, for example)?
       • Family history of BRCA/Lynch syndrome cancers may prompt genetic screening in patient
  4. Patient preference for investigations/treatment
     • Benefits/harms of treatment (sexual function, for example)
• Physical exam
  • Body habitus
    • Determine candidacy for intervention
  • Digital rectal examination
    • A palpable tumour and the extent is associated with local disease extent (clinical T stage)
    • In a screened population, an abnormal DRE is also associated with an increased risk for detecting high-grade (Gleason 8 to 10) prostate cancer
    • Can both overestimate and underestimate the extent of disease because of its poor sensitivity and lack of reproducibility
    • Consider useful to detect presence, but not useful to assess stage
    • When DRE and PSA tests are used in prostate cancer screening, detection rates are higher with PSA testing alone vs. DRE alone, and highest with the tests together
      • See below in Labs/PSA/Landmark Studies
      • The 2018 AUA and 2017 CUA Guidelines support the role of DRE in screening

Labs

PSA[1]

• Serum PSA is the single test with the highest positive predictive value for prostate cancer
  • Although as many as 20-30% of males evaluated for an elevated PSA level may be diagnosed with prostate cancer after TRUS biopsy, as many as 70-80% will not be found to have cancer
• PSA Basics
  • Discovered in 1979
  • Member of kallikrein gene family
  • An enzyme (serine protease) which functions to liquify semen
  • Molecular weight: 33-kD
    • Begins as 17-amino acid chain preproPSA --> cleavage results in inactive proPSA --> cleavage by hK2 results in active form PSA
  • Primarily produced by prostatic luminal epithelial cells
    • Has been detected in other body fluids and tissues: in females, PSA is found in female ejaculate at concentrations roughly equal to that found in male semen; other fluids with high concentrations of PSA include breast milk and amniotic fluid.
    • Ectopic expression of PSA occurs in normal breast tissue, and tumours of the adrenals, kidneys, colon, ovaries, liver, and parotid[2]
  • Expression is strongly influenced by androgens; becomes detectable at puberty with increasing levels of luteinizing hormone and testosterone
    • Clinical implication: in hypogonadal men with low testosterone levels, serum PSA level may be low because of decreased expression and may not reflect the presence of prostate disease such as cancer
  • Half-life: 2-3 days[3][4]
  • Circulates in bound/complexed (70-80%) and unbound/free (20-30%) forms
    • Bound/complexed PSA
      • Proteins that bind PSA in blood (3):
        1. α1-antichymotripson (ACT)
           • Binds most PSA in an irreversible fashion
           • Detectable form of bound PSA
        2. α2-macroglobulin (A2M)****#*Binds 5-10% of PSA
           • PSA-A2M complex undetectable by most current assays
        3. α1-protease inhibitor (API)
           • Binds 1-2% of PSA
           • Detectable form of bound PSA (to a lesser extent than PSA bound to ACT)
    • Free PSA
      • Rendered inactive within the prostatic epithelial cell before release into the serum
      • Isoforms (3):
        1. Intact PSA
        2. BPH-associated PSA (BPSA)
           • Generally limited to transition zone tissue
        3. proPSA
           • Uncleaved free PSA molecule with a leader sequence (see above)
           • Evaluated as a marker with conflicting results
           • Exists in 3 forms: -2proPSA, -4proPSA, -7proPSA
        4. Normally, these isoforms exist in equal concentrations
           • BPSA is highly expressed in BPH
           • proPSA is highly expressed in prostate cancer

Causes of elevated PSA

1. Prostate disease (BPH, prostatitis, prostate cancer, etc.)
2. Prostate manipulation (prostate massage, biopsy, etc.)

• Prostate Disease
  • Prostate cancer
    • Prostate cancer cells produce less PSA than normal prostatic tissue
    • PSA becomes elevated in prostate cancer due to disruption of cellular architecture within the prostate gland
      • Prostate cancer lacks basal cells, resulting in the disruption of the basement membrane and normal lumen architecture
    • PSA levels are inversely correlated with risks of
      • Pathologically organ-confined disease
        • PSA < 4.0 ng/mL: 80%
        • PSA 4-10 ng/mL: 66%
        • PSA > 10.0 ng/mL: <50%
      • Pelvic lymph node involvement
        • PSA >20 ng/ml: 20%
        • PSA >50 ng/mL: 75%
• Prostate manipulation
  • May influence PSA in a clinically meaningful way
    1. Biopsy[5][6]
       • Results in immediate elevation in the serum PSA level, with a median increase of 6-8 ng/mL
       • Usually returns to a stable, baseline level within 2-3 weeks
    2. TURP[7][8]
       • Results in immediate elevation in the serum PSA level, with a median increase of 6-13 ng/mL[9]
       • Usually returns to a stable, baseline level within 2-3 weeks[10]
    3. Ejaculation
       • Studies examining the effect of ejaculation on serum PSA have reported conflicting results.
       • A repeat PSA test after 48 hours of sexual abstinence may be helpful for interpreting serum PSA levels that are minimally elevated or newly elevated.
    4. Long-distance cycling
       • PSA levels increasing by ≈10% after bicycle rides > 55km
  • Unlikely to influence PSA in a clinically meaningful way
    1. DRE
       • Can lead to slight increases in serum PSA level; however, the resultant change in PSA values falls within the error of the assay and rarely causes false-positive test results
    2. Cystoscopy[11][12]
       • Results in small (0.05-0.15 ng/mL) increase in PSA
       • Serum PSA determination after either a flexible or a rigid cystoscopy is accurate and reliable
    3. TRUS[13]
       • Results in small (0.3 ng/mL) increase in PSA
       • Serum PSA determination after TRUS without biopsy is accurate and reliable
    4. Urethral catheterization
       • Very little effect on PSA level
       • In patients with urethral catheter, routine evaluation of PSA rising should be considered.[14]
  • Most of the rise in total PSA after prostate manipulation is contributed by the free (non-bound) component.
    • In general, complexed PSA is the most stable component and relatively little rise occurs following prostate manipulation.

Clinical factors that influence PSA

• In the absence of prostate cancer, PSA levels vary with (4):
  1. Age
  2. Race
     • African-American males without prostate cancer have higher PSA values than Caucasians
  3. Prostate volume
     • PSA increases 4%/mL prostate volume
       • BPH surgery can lead to reductions in the serum PSA level
       • Annual rate of change in PSA is higher in men with BPH compared to men without BPH
  4. BMI
     • Increasing BMI independently associated with decreasing serum PSA

PSA-derivatives

• Concept is to adjust for known factors that can influence PSA (age, volume, race (BMI can also influence PSA)) and improve specificity
  • Patients with prostate cancer may have a “normal” PSA (i.e. false-negative) and patients without prostate cancer may have "elevated" PSA (i.e. false-positive); PSA is neither sensitive nor specific, particularly between 4.0-10.0 ng/dL.

Volume-adjusted PSA

• Concept is to reduce confounding from BPH
• Includes PSA divided by prostate volume (PSA density, PSAD), complexed PSAD (cPSA divided by prostate volume), and PSA transition zone density (PSA divided by transition zone volume, PSAT)
  • A PSAD of ≥0.15 has been proposed for recommending prostate biopsy in men with PSA levels between 4-10 ng/mL and normal DRE
  • PSAT has been developed to adjust for the transition zone volume, the major determinant of serum PSA in men without prostate cancer
• Prostate volume typically determined by US

Age-/race- adjusted PSA

• Race: African-American men without prostate cancer have higher PSA values than Caucasian men
• Age: PSA normally increases with age
  • The mature prostate is between 20-25 g and remains relatively constant until ≈age 50, when the gland enlarges in many men; the average prostate volume in a 60-70 year old is ≈48 g

PSA velocity

• Short-term fluctuations in PSA can occur between measurements in the presence or absence of prostate cancer, primarily as a result of physiologic variation. However, the rate of change in PSA (PSAV)—PSA corrected for the elapsed time between measurements is associated with the risk for prostate cancer
• PSAV > 0.75 ng/mL/year has been shown to be a specific marker for the presence of prostate cancer in men with PSA levels between 4-10 ng/mL
• There are conflicting studies on whether PSAV provides more information than total PSA in predicting disease aggressiveness

Free-PSA (fPSA)

• %fPSA varies directly with age and volume, and indirectly with total PSA. Does not vary by race.
• Low %fPSA is associated with increased risk of prostate cancer
  • PSA produced by malignant cells escapes proteolytic processing more frequently, resulting in a greater fraction of serum PSA complexed to α1-antichymotrypson and a lower %fPSA compared to men without cancer
  • Catalona et al. (1998)
    • Population:
      • Prospective cohort study of 773 men aged 50-75 enrolled primarily through screening centers with PSA 4-10 and palpably benign gland that underwent diagnostic biopsy
        • 49% had cancer, 51% had benign disease
    • Primary outcome:
      • %fPSA that maintained 95% sensitivity for PC detection
    • Results:
      • %fPSA was inversely associated with risk of cancer
      • AUC 0.72 %fPSA vs. 0.53 total PSA
      • %fPSA cut-off:
        • ≤25: sensitivity: 95%, specificity 20%
        • ≤22: sensitivity 90%, specificity 29%
      • INSERT FIGURE
    • Catalona, William J., et al. "Use of the percentage of free prostate-specific antigen to enhance differentiation of prostate cancer from benign prostatic disease: a prospective multicenter clinical trial." Jama 279.19 (1998): 1542-1547.
  • %fPSA as a test is FDA-approved in men with a total PSA 4-10ng/mL and negative DRE
    • %fPSA is most useful in the setting of PSA levels < 10ng/ml because the PPV of tPSA > 10- 20ng/ml has been shown to be ≈80%; it’s utility in PSA <4.0ng/ml is unknown
    • No %fPSA threshold has been established, proposed cut points generally range from 15-25%
    • Debate remains surrounding the utility of %fPSA as a prognostic biomarker
• Complexed-PSA (as opposed to the free-PSA)
  • Overall, at a high sensitivity, cPSA provides higher specificity than tPSA and comparable specificity to %fPSA in prostate cancer detection. A potential advantage of cPSA is the requirement for one assay
• 5ARIs lower total PSA levels by ≈50% after 12 months of treatment
  • With the use of 5ARIs, fPSA decreases in a similar fashion to tPSA, and the %fPSA is not altered significantly
  • Finasteride 1 mg (Propecia) used for male pattern hair loss (androgenic alopecia) results in the same decline in serum PSA levels as the 5-mg dosage used for the treatment of BPH
  • In the PCPT trial, PSA had statistically significantly better sensitivity and AUC for detecting prostate cancer in the finasteride arm[15]

Other prostate cancer biomarkers

• See Prostate Cancer: Blood, Urine and Tissue-based markers

Imaging

Primary

Transrectal ultrasound (TRUS)

• Compared to DRE, TRUS does not improve the ability to stage prostate cancer
• In general, TRUS under-stages rather than over-stages prostate cancer
• Limited detection of transition zone lesions

Magnetic Resonance Imaging (MRI)

• See Video on Approach and Principles to Prostate MRI
• MRI uses strong magnetic fields and the electromagnetic properties of hydrogen protons to generate the signal that is used to create images[16]
  • Signal intensities vary based on the hydrogen content of the tissue
  • For details, see Pooley, Robert A. "Fundamental physics of MR imaging." Radiographics 25.4 (2005): 1087-1099.

Imaging sequences

• Sequences relevant for prostate imaging
  • T1-weighted imaging (T1WI)
  • T2-weighted imaging (T2WI)
  • Diffusion weighted imaging (DWI) with apparent diffusion coefficient (ADC) maps
  • Dynamic contrast enhanced (DCE) imaging
  • Magnetic resonance spectroscopic imaging (MRSI)
• Multi-parametric (mpMRI) is the combination of multiple MRI sequences
• In prostate cancer, the primary diagnostic parameters are (2):[17]
  • T2WI
  • DWI with ADC maps
• T2WI
  • Captures the movement of protons in the xy-axis (transverse)
  • Primary uses (3):
    1. Visualization of zonal and anatomical features of the prostate.
       • See Figure
    2. Optimal sequence to evaluate lesions in the transition zone[18]
    3. Optimal sequence in establishing the anatomic relation of the tumor with critical structures, such as the prostatic capsule and neurovascular bundles.[19]
  • Signal intensity
    • High intensity
      • Fluids (CSF, urine)
      • Fat
      • Normal peripheral zone (due to its high water content)
      • Seminal vesicles
    • Intermediate intensity
      • Central zone
        • Clinical implication: differential diagnosis of intermediate/low intensity lesions on T2 at the base of prostate and paramedian includes central zone that is being pushed out by BPH nodules of transition zone or cancer
    • Low intensity (7): CHAPPSS
      1. Prostate Cancer
         • As 70% of all prostate cancers occur within the peripheral zone, the tissue characteristics allow for T2WI to detect a significant number of tumors in this zone
      2. Hemorrhage
         • Post-biopsy hemorrhage can interfere with tumor detection[20], since areas of hemorrhage appear similar to cancer on T2WI
           • If obtaining prostate MRI post-biopsy, a delay of 6-8 weeks after biopsy is recommended; but even with this delay, significant hemorrhage may be discovered, and, if present, the examination should be rescheduled[21]
         • Can be distinguished from cancer with T1WI (hemorrhage has high intensity on T1WI, cancer has low intensity on T2WI)
      3. Prostatitis
      4. Atrophy
      5. Post-treatment changes
      6. Scars
      7. Stromal hyperplasia i.e. benign prostatic hyperplasia (BPH)
         • Clinical implication: On T2WI, BPH nodules can be difficult to distinguish from cancer
  • Lesion shape
    • Wedge-shaped/linear lesions are more likely benign
• Diffusion weighted imaging (DWI)
  • Measures the diffusion of water protons within tissue
    • In normal water-rich glandular tissue, protons are mobile
    • In densely packed water-poor tissue such as that found in tumors, protons have restricted movement.
  • Images are acquired by sequentially applying multiple magnetic field gradients, known as b-values, to calculate ADC values and construct ADC maps.
    • b-value is a factor that reflects the strength and timing of the gradients used to generate diffusion-weighted images. The higher the b-value, the stronger the diffusion effects.
      • Typical b-values available on modern MRI scanners range from 0 to about 4000 s/mm²[22]
    • ADC values are calculated by the software and displayed as a parametric map reflecting the degree of diffusion of water molecules through different tissues.
      • Different b-values will produce different ADC maps
      • In general, ADC values decrease when b-values increase above 1000 s/mm²[23]
  • Primary use:
    • Optimal sequence to evaluate lesions in the peripheral zone[24]
  • Signal intensity
    • ADC maps
      • Intermediate intensity
        • Normal glandular prostate tissue allows unrestricted free water movement
      • Low intensity
        • Prostate cancer[25]
          • Appears as high signal intensity focus on high b-value images
            • Image with highest b-value (lowest ADC) likely to be most useful
          • Tumors with the higher restriction (low ADC values) tend to be higher grade
• T1WI
  • Captures the movement of protons in the z-axis
  • Primary uses (2):
    1. Optimal sequence to identify areas of hemorrhage within the prostate
    2. Often used to look at normal anatomical details.
  • Signal intensity
    • High intensity
      • Hemorrhage/blood has high signal intensity on T1, against a homogenous low signal background.
      • Fat
    • Low intensity
      • Fluids (CSF, urine)
      • Prostate cancer
• Dynamic contrast enhancement (DCE)
  • A series of T1WI obtained before, during, and after the injection of intravenous gadolinium-based contrast media
  • Primary use (1):
    • Measures the vascularity of prostate tissue.
      • Focal early hyperenhancement is suggestive of a malignancy
        • Tumors have increased vascularity due to neo-angiogenesis and, therefore, take up the contrast agent more rapidly than normal tissue. Moreover, this contrast washes out of tumor regions quickly leading to a steep wash-in-wash-out enhancement curve.
        • There is considerable overlap of with benign conditions, such as benign prostatic hyperplasia and prostatitis.
          • DCE MRI is most helpful when the T2W MRI and DWI are equivocal.
            • In these cases, strong early enhancement or rapid washout of contrast media from the lesion increases the suspicion that the lesion is a clinically significant malignancy.
      • Very useful in detecting sites of recurrent prostate cancer after prostatectomy or radiation therapy where focal enhancement may indicate a site of focal recurrence
• Magnetic resonance spectroscopic imaging (MRSI)
  • Uses the relative concentration of cellular metabolites in the prostate, specifically citrate and choline, to detect prostate cancer.
    • Citrate is a marker of normal prostatic tissue, whereas high levels of choline can be found in cancerous cells owing to increased cell turnover, which, in turn, leads to an increased choline-to-citrate ratio in patients with prostate cancer
  • When combined with T2WI, MRSI has been found to have the highest sensitivity of all MRI sequences (92%) in detecting prostate cancer.
  • While MRSI is a promising imaging sequence, it requires an extra 10 to 15 minutes of examination time. Also, for this phase an endorectal coil (see below) is mandatory at 1.5T and optional at 3T. For these reasons, MRSI is less commonly performed than other mpMRI sequences in prostate MRI studies.
• Bi-parametric MRI (bpMRI)
  • Combination of only non-contrast T2WI and DWI (with ADC maps) series
  • Advantages[26]
    • Can be performed without an endorectal coil
    • Can be performed intravenous access and contrast administration
    • Fewer sequences reduces time/costs to complete study
      • Requires less than half the in-bore magnet time to perform compared with the complete mpMRI
  • Disadvantages
    • Fewer imaging sequences which may limit adequate interpretation
  • No significant difference in sensitivity or specificity compared to mpMRI
    • Systematic review and meta-analysis (2018)
      • 20 studies involving 2142 patients
      • Results
        • No significant difference in pooled sensitivity and specificity
          • Sensitivity: 0.74 (95% CI, 0.66–0.81) bpMRI vs. 0.76 (95% CI, 0.69–0.82) mpMRI
          • Specificity: 0.90 (95% CI, 0.86–0.93) bpMRI vs. 0.89 (95% CI, 0.85–0.93) mpMRI
      • Woo, Sungmin, et al. "Head-to-head comparison between biparametric and multiparametric MRI for the diagnosis of prostate cancer: a systematic review and meta-analysis." American Journal of Roentgenology (2018): W226-W241.

Magnet strength

• mpMRI can be performed at field strengths of 1.5T or 3T with or without an endorectal coil.
  • 3T magnets reduce image acquisition time and improve spatial resolution
  • Greater magnet strength does not necessarily mean greater cancer detection rates.

Endorectal coil

• Advantages
  • Improves image resolution by increasing the SNR
    • Standard clinical field strengths of 1.5T do not provide sufficient signal-to-noise ratio for clinical diagnosis of prostate cancer. To compensate for this deficiency, the use of surface and/or endorectal coil arrays has been proposed
    • There is consensus regarding the use of a surface body coil and an endorectal coil at 1.5T but controversy remains regarding the need for an endorectal coil at 3T.
      • The highest signal-to-noise ratio (SNR) is achieved at 3T with an endorectal coil but acceptable results can be achieved at 3T without an endorectal coil.
• Disadvantages
  • Patient discomfort
  • Additional time required for proper placement and verification
  • Cost
  • Deformation of the gland which may affect the image registration for targeted biopsy or radiation planning
    • Concerns regarding alterations in prostate volume have largely been dispelled.

Prostate Imaging and Reporting Archiving Data System (PI-RADS)

• Provides guidance for interpretation of different sequences and prostate zones
• Introduced in 2012, revised in 2015 (version 2.0)
• Each lesion is scored, using a 5-point scale based on the likelihood (probability) that mpMRI findings correlate with the presence of a clinically significant cancer
  • Clinically significant cancer is defined on pathology/histology as (3):[27]
    1. Gleason score ≥7 (including 3+4 with prominent but not predominant Gleason 4 component) and/or
    2. Volume ≥0.5cc and/or
    3. Extra prostatic extension(EPE).
  • Detection rates by PI-RADS score for any prostate cancer[28]
    • PR 1-2: 15%
    • PR 3: 25%
    • PR 4: 58%
    • PR 5: 85%
  • Positive predictive values for ISUP grade group ≥2 based on PI-RADS score:[29]
    • PI-RADS 1-2: 7%[30]
    • PI-RADS 3: 12–15%
    • PI-RADS 4: 39–48%
    • PI-RADS 5: 72%
  • If PIRADS[31]
    • ≥4 or 5, biopsy should be considered
    • ≤3, biopsy may or may not be appropriate, depending on factors other than mpMRI alone
• Lesions in the peripheral zone appear round or irregular, and are focally hypointense, whereas transition zone lesions are non-circumscribed and moderately hypointense, and may exhibit a characteristic ‘‘erased charcoal’’ sign.

Test Characteristics

• Cochrane Systematic Review and Meta-analysis (2019)
  • MRI compared with template‐guided biopsy
    • Detection of grade 2 or higher prostate cancer
      • Sensitivity: 0.91 (95% CI 0.83 to 0.95)
      • Specificity: 0.37 (95% CI 0.29 to 0.46)
    • Detection of grade 3 or higher prostate cancer
      • Sensitivity: 0.95 (95% CI 0.87 to 0.99)
      • Specificity: 0.35 (95% CI 0.26 to 0.46)
  • Drost, Frank‐Jan H., et al. "Prostate MRI, with or without MRI‐targeted biopsy, and systematic biopsy for detecting prostate cancer." Cochrane Database of Systematic Reviews 4 (2019).
• PROMIS (2017)
  • Objective: evaluate sensitivity/specificity of prostate MRI vs. standard TRUS biopsy, with template prostate mapping biopsy as gold standard reference
  • Population: 576 men with a clinical suspicion of prostate cancer (elevated serum PSA (up to 15 ng/mL) within previous 3 months, suspicious digital rectal examination, suspected organ confined stage T2 or lower on rectal examination, or family history) and no previous prostate biopsy
  • Intervention: prostate MRI followed by template prostate mapping biopsy as gold standard reference and then standard TRUS biopsy
    • MRI was done with 1.5 Tesla magnet
    • Patients with positive MRI did not undergo targeted biopsy
  • Primary outcomes: sensitivity and specificity of prostate MRI vs. standard TRUS biopsy for detection of clinically significant prostate cancer
    • Clinically significant prostate cancer defined as Gleason score ≥4 + 3 or a maximum cancer core length 6 mm or longer
  • Results:
    • mpMRI displayed a moderate sensitivity (88%) and negative predictive value (76%), but poor specificity (45%) and positive predictive value (65%).
  • Authors' interpretation: MP-MRI, used as a triage test before first prostate biopsy, could reduce unnecessary biopsies by ≈25% (based on negative-predictive value). MP-MRI can also reduce over-diagnosis of clinically insignificant prostate cancer and improve detection of clinically significant cancer.
  • Ahmed, Hashim U., et al. "Diagnostic accuracy of multi-parametric MRI and TRUS biopsy in prostate cancer (PROMIS): a paired validating confirmatory study." The Lancet 389.10071 (2017): 815-822.

Advantages

• Compared to pathway of elevated PSA to TRUS-guided biopsy without MRI, pathway of elevated PSA to MRI with targeted biopsy
  • Improves identification of anterior tumors
  • Reduces over diagnosis of clinically insignificant prostate cancer
  • Increases diagnosis of clinically significant prostate cancer
    • ≈10% (but up to 20%) of negative MRI have clinically significant prostate cancer
• PRECISION (2018)
  • Objective: in males with clinical suspicious of prostate cancer, determine whether prostate MRI with targeted biopsy only can increase detection of clinically significant prostate cancer and decrease detection of clinically insignificant prostate cancer
  • Design: Non-inferiority trial
  • Population: 500 males with clinical suspicion of prostate cancer based on elevated PSA or abnormal DRE
  • Randomized to standard TRUS–guided biopsy vs. MRI +/- targeted biopsy
    • Males in the MRI group underwent a targeted biopsy (without standard biopsy cores) if the MRI was suggestive of prostate cancer; if MRI results were not suggestive of prostate cancer, males were not offered biopsy
  • Outcomes
    • Primary: proportion of males who received a diagnosis of clinically significant cancer
    • Secondary: proportion of males who received a diagnosis of clinically insignificant cancer
  • Results:
    • MRI-targeted biopsy was non-inferior and superior to detecting clinically significant cancer (absolute risk difference 12%, 38% MRI vs. 26% standard TRUS)
    • MRI-targeted biopsy was associated with fever patients being diagnosed with clinically insignificant cancer (absolute risk difference -13%)
  • Authors’ conclusion: Using MP-MRI to triage men might allow 27% of patients avoid a primary biopsy and diagnosis of 5% fewer clinically insignificant cancers. If subsequent TRUS-biopsies were directed by MP-MRI findings, up to 18% more cases of clinically significant cancer might be detected compared with the standard pathway of TRUS-biopsy for all. MP-MRI, used as a triage test before first prostate biopsy, could reduce unnecessary biopsies by a quarter. MP-MRI can also reduce over-diagnosis of clinically insignificant prostate cancer and improve detection of clinically significant cancer.
  • Kasivisvanathan, Veeru, et al. "MRI-targeted or standard biopsy for prostate-cancer diagnosis." New England Journal of Medicine 378.19 (2018): 1767-1777.
• STHLM3 - MRI-targeted vs. standard biopsy in prostate cancer screening
  • Population: 1532 males aged 50-74 years with screening PSA > 3 ng/mL
    • Screening population in STHLM3, compared to patients referred for abnormal PSA or DRE in PRECISION
  • Randomized to standard TRUS-guided biopsy vs. MRI and if MRI positive then standard biopsy with targeted biopsy
    • If MRI negative, biopsies were not performed unless Stockholm3 test scores ≥25% or greater
  • Primary outcome: proportion of males diagnosed with clinically significant cancer (Gleason score ≥7)
  • Secondary outcome: proportion of males diagnosed with clinically insignificant cancers (Gleason score 6).
  • Results
    • MRI non-inferior to diagnose clinically significant disease (21% MRI vs. 18% standard biopsy)
    • Significantly fewer clinically insignificant disease with MRI (4% MRI vs. 12% standard biopsy)
  • Eklund, Martin, et al. "MRI-targeted or standard biopsy in prostate cancer screening." New England Journal of Medicine (2021).

Disadvantages

• Availability/cost
• Interobserver reproducibility remains a challenge.[32]
• Learning curve related to reading MRI and to performing fusion biopsies
• Use of MRI for tumor staging remains controversial.
  • Variable sensitivities (13-91%) and specificities (49-97%) have been reported for predicting extra-capsular extension.

Guidelines on Use of MRI

• 2023 NCCN (PROSD-3)
  • Multiparametric MRI is strongly recommended, if available [before biopsy]
• 2022 EAU[33]
  • Systematic biopsy is an acceptable approach in case MRI is unavailable
• 2017 Cancer Care Ontario Guidelines
  • Biopsy-naïve: MRI should not be considered standard of care
  • Prior negative biopsy: MRI followed by targeted biopsy may be considered

Targeted biopsy only vs. targeted and systematic

• MRI-FIRST (2019)
  • Objective: determine whether biopsy of MRI detected lesions increases detection of clinically significant prostate cancer compared to standard biopsy i.e. can we omit standard biopsy and do only targeted biopsy?
  • Design: paired-diagnostic study (non-randomized)
  • Population: 275 patients with clinical suspicion of prostate cancer
  • Intervention: MRI followed by standard systematic biopsy then targeted biopsy of up to 2 lesions on MRI. Patients with negative multiparametric MRI (Likert score ≤2) had systematic biopsy only.
  • Primary outcome: detection of clinically significant prostate cancer
  • Results:
    • No difference in detection of clinically significant prostate cancer (30% systematic biopsy vs. 32% targeted biopsy)
    • Clinically significant prostate cancer would have been missed in 5% of patients had systematic biopsy not been done, and in 8% of patients had targeted biopsy not been done
  • Obtaining a multiparametric MRI before biopsy in biopsy-naive patients can improve the detection of clinically significant prostate cancer compared to systematic biopsy alone but does not seem to avoid the need for systematic biopsy
  • Rouvière, Olivier, et al. "Use of prostate systematic and targeted biopsy on the basis of multiparametric MRI in biopsy-naive patients (MRI-FIRST): a prospective, multicentre, paired diagnostic study." The Lancet Oncology 20.1 (2019): 100-109.
• Ahdoot et al. (2020)
  • Study design: cohort study
  • Population: 2103 males with an elevated PSA or abnormal DRE with a positive MRI underwent a targeted and systematic biopsy
  • Outcomes:
    • Primary outcomes: cancer detection rates by grade group for each biopsy method
  • Results
    • Use of MRI-targeted biopsy led to more diagnoses of cancers in grade groups 3, 4, and 5 than systematic biopsy and fewer cancers in grade group 1
    • The addition of MRI-targeted biopsy to systematic biopsy led to 208 (9.9%) more prostate cancer diagnoses. Of these new diagnoses, 59 (28.4%) were clinically significant (grade group ≥3) disease.
    • MRI-targeted biopsy was responsible for upgrading of events in 458 patients (21.8%) when added to systematic biopsy
    • MRI-targeted biopsy alone without systematic biopsy would have led to no detection of cancers of grade group 2 or higher in 123 patients (5.8%) and no detection of cancers of grade group 3 or higher in 41 patients (1.9%)
    • Among the patients who underwent radical prostatectomy, upgrading on histopathological analysis after undergoing combined biopsy occurred 14% of patients. The rates of any upgrading or clinically significant upgrading on whole-mount histopathological analysis were substantially higher for systematic biopsy and MRI-targeted biopsy (30.9% and 8.7%, respectively) than for combined biopsy
  • Authors' interpretation: Among patients with MRI-visible lesions, combined biopsy led to more detection of all prostate cancers. However, MRI-targeted biopsy alone underestimated the histologic grade of some tumors. After radical prostatectomy, upgrades to grade group 3 or higher on histopathological analysis were substantially lower after combined biopsy.
  • Ahdoot, Michael, et al. "MRI-targeted, systematic, and combined biopsy for prostate cancer diagnosis." New England Journal of Medicine 382.10 (2020): 917-928.
• GOTEBORG-2 (2022)
  • Objective: Determine whether targeted-biopsy only (and avoid systematic) is adequate in patients with elevated PSA and prostate MRI
  • Population: Swedish males aged 50-60 living in Gothenburg, Sweden, without previous diagnosis of prostate cancer
  • Randomized to invited screening with PSA test vs. no invitation
    • If PSA > 3 ng/mL, patients underwent prostate MRI
      • Further randomized to
        • Reference group: Systematic (regardless of MRI results) +/- targeted biopsy if MRI positive (PR3-5) vs.
        • Experimental group: Targeted biopsy only if MRI positive (PR3-5) (experimental group); If PSA>10, patients underwent systematic biopsy, with or without targeted biopsy, regardless of MRI results
          • If low-grade prostate cancer (mainly with Gleason 3+3 cancer but also some with Gleason 3+4 cancer) detected by targeted biopsy in the experimental group, were invited to undergo follow-up systematic biopsy. The Gleason score was thus based on both targeted and systematic biopsies after a cancer diagnosis in both groups in order to avoid sampling bias due to different primary biopsy techniques.
  • Outcomes:
    • Primary outcome: detection of clinically insignificant prostate cancer, defined as a Gleason score of 3+3.
    • Secondary outcome: detection of clinically significant prostate cancer, defined as a Gleason score of 3+4 or higher
  • Results:
    • 17,980 (47%) of those randomized to invitation to screening underwent PSA testing
      • 7% had PSA > 3 ng/mL
        • 95% of patients with PSA > 3 ng/mL underwent MRI
    • Clinically insignificant prostate cancer: significantly more common in patients undergoing systematic +/- targeted biopsy compared to targeted biopsy only (1.2% vs. 0.6%)
    • Clinically significant prostate cancer: no significant difference (1.1% systematic +/- targeted vs. 0.9% targeted biopsy only)
    • 10 patients in reference group found to have clinically significant prostate cancer on systematic only
      • 9 with negative MRI, 1 with false-positive MRI
        • All GG2, GG4 <5% in 6 patients
          • 6 managed with AS
    • 128 patients in experimental group with PSA <10 diagnosed with cancer by targeted biopsy only
      • 72/128 (56%) had GG1
        • 86% underwent systematic biopsy
        • 26% upgraded (all GG2 except 1 to 3+5)
      • Gleason 3+3 lesions that had been detected by systematic biopsy differed only in tumor extension from those that had been detected by targeted biopsy of suspicious lesions shown on MRI, with greater volume measured in tumors that were visible on MRI
  • Author's interpretation: The avoidance of systematic biopsy in favor of MRI-directed targeted biopsy for screening and early detection in persons with elevated PSA levels reduced the risk of overdiagnosis by half at the cost of delaying detection of intermediate-risk tumors in a small proportion of patients.
  • Hugosson, Jonas, et al. "Prostate cancer screening with PSA and MRI followed by targeted biopsy only." New England Journal of Medicine 387.23 (2022): 2126-2137.

Biopsy after Negative MRI

• ≈10% (but up to 20%) of negative MRI have clinically significant prostate cancer
• Predictors of clinically significant prostate cancer in presence of negative MRI[34]
  • PSA density > 0.15 ng/ml/cc[35][36]
  • History of previous negative biopsy[37]
  • Abnormal DRE[38]/Clinical stage T2a or greater[39]
  • Prostate cancer family history[40]

Modalities under investigation

• Positron Emission Tomography (PET)
  • One potential advantage of PSMA PET over mpMRI is that interpretation is not influenced by biopsy-related artifacts such as hemorrhage or inflammation
• Multiparametric Ultrasonography
  • Contrast-enhanced (CE) TRUS produces a detailed image of microvascular distribution within the prostate using highly echogenic microbubble contrast agents that are minute enough to flow within capillaries.

Metastasis

"Conventional" imaging

• Regional
  • CT/MRI is used for regional lymph node staging
• Distant
  • Radionuclide bone scan (bone scintigraphy) is the most commonly used test for the detection of skeletal metastases

Novel Positron Emission Tomography (PET)-CT imaging[41]

• PET scans use a radioactive tracer to show both normal and abnormal metabolic activity.
  • Use of either hybrid PET/computed tomography (CT) or PET/magnetic resonance (MR) scanners with PSMA-targeted radiopharmaceuticals allows anatomical localization and characterization of PSMA-avid lesions
• Advantage over conventional imaging
  • Higher sensitivity for the detection of prostate cancer recurrence and metastases at low PSA values (<2.0ng/mL).
    • 38% of PSMA-targeted PET scans show disease sites in males with PSA <0.5 ng/ml[42]
  • 18F-PET provides the best sensitivity and specificity for the detection of bony metastases in prostate cancer

Prostate cancer PET radiopharmaceutical tracers

• Not PSMA-specific radiopharmaceutical tracers
  • Examples include 18F-fluciclovine (trade name Axumin), 18F-fluorodeoxyglucose (FDG), and 11C-choline
    • 18F-fluciclovine FDA approved in 2016
  • Replaced by PSMA-specific tracers
    • Lower sensitivity and specificity than PSMA-specific ligands
      • In a 2019 prospective study of males who had undergone prostatectomy and had a rising PSA still under 2.0ng/mL, 68Ga-PSMA-PET detected occult metastases 4.54x significantly more frequently than 18F-fluciclovine-PET[43]
• PSMA-specific radiopharmaceuticals tracers
  • PET tracers that bind to Prostate-Specific Membrane Antigen (PSMA)
    • PSMA
      • Also known as glutamate carboxypeptidase II (GCP II)
      • A transmembrane glycoprotein
      • Highly overexpressed in >90% of prostate cancers
        • Increased expression with
          • Increased pathological Gleason grade
          • Castrate-resistance
  • PSMA-specific radiopharmaceutical tracers used in prostate cancer (2):
    • Fluorine-18 (18F)-labeled PSMA-specific (18F-DCFPyL (trade name Pylarify), 18F-PSMA-1007)
      • Most commonly used radiotracer in the US and (18F-DCFPyL) Canada
      • 18F-DCFPyL adverse reactions: headache, altered taste, fatigue[44]
    • Gallium-68 (68Ga)-labeled PSMA-specific
      • High specificity and sensitivity
        • Outperforms standard CT and MRI in detection of nodal and osseous metastases.
      • As of May 2021, only available locally at two sites in California[45]
      • Excretion: urinary
  • Uptake of PSMA-specific radiopharmaceuticals[46]
    • Physiological
      • High uptake: lacrimal and salivary glands, kidneys
      • Moderate uptake: spleen, nasopharynx
      • Variable uptake: vocal cords, trachea, bronchi, proximal GI tract
      • Uptake also seen in central nervous system and peripheral nervous system (ganglia and nerve routes)
        • Celiac and stellate ganglia may be false-positives for retroperitoneal and supraclavicular lymphadenopathy
    • Benign disease
      1. Infectious and inflammatory processes (e.g., sarcoidosis)
         • Increased blood flow and vascular permeability may partly explain the increased PSMA uptake in inflammatory conditions.
      2. Benign neoplasms (mesenchymal tumors (vascular, neurogenic, connective tissue origin) and epithelial tumors (edenoma and thymoma))
      3. Bone remodelling (healing fractures, degenerative or arthritic processes (e.g., osteophytes), Paget's disease)
      4. Amyloidosis
    • Malignancy
      • Prostate cancer
      • Non-prostate malignancies
        • Renal cell carcinoma, leiomyosarcoma, thyroid cancer, nasopharyngeal cancer, GI tract cancer, breast cancer, neuroendocrine cancer
  • Clearance of PET tracers used in prostate cancer[47]
    • Most are cleared via the urinary tract, with high accumulation in the urinary tract and bladder and moderate uptake in the liver
      • Exception: 18F-PSMA-1007, 18F-fluciclovine, and 11-choline are cleared primarily by the hepatobiliary tract, with higher uptake in the liver, and little accumulation in the ureters and bladder
        • Clinical implication: since 18F-PSMA-1007, 18F-fluciclovine, and 11-choline have minimal excretion from the urinary tract, use of these tracers may aid in identifying disease sites adjacent to the bladder and ureters, such as local tumor recurrence after prostatectomy.
  • Causes of false-negative PSMA-targeted PET
    1. Small tumor volume
       • May be seen in early-stage biochemical recurrence when the serum PSA <0.5 ng/ml
    2. Neuroendocrine differentiation of prostate cancer with downregulation of PSMA expression
       • Neuroendocrine differentiation occurs in 5–10% of prostate cancers overall and approximately 30% of men with advanced disease
    3. Androgen receptor inhibition
       • Short-term ADT likely increases PSMA-targeted PET positivity, whereas prolonged, continuous ADT is associated with a higher likelihood of a negative PSMA-targeted PET

Potential roles of PSMA-PET imaging in prostate cancer

1. Primary staging of high-risk prostate cancer
   • proPSMA (2020)
     • Objective: determine whether PSMA PET-CT prior to treatment in patient with high risk prostate cancer increases detection of metastases, compared to conventional imaging
     • Population: 300 males with high-risk (PSA ≥20, grade group ≥3, or ≥cT3) prostate cancer being considered for radical prostatectomy or radiotherapy
     • Randomized to Ga-PSMA-11 PET-CT vs. conventional imaging (CT and bone scan), followed by second-line cross-over imaging.
       • Second-line cross-over imaging was done within 14 days of baseline imaging, unless ≥3 distant metastases identified on first-line imaging.
       • At 6 months, patients underwent repeat imaging as per randomised group with cross-over if
         • Baseline imaging evidence of metastasis (N1 or M1)
         • Biochemical or clinical suspicion of residual or recurrent disease.
       • Primary outcome: accuracy (based on area under the curve (AUC)) of first-line imaging at identifying either pelvic nodal or distant metastatic disease, compared to assessment of metastases at 6 months (reference standard)
         • Metastatic disease disease was defined by hard and soft criteria based on histopathologic, imaging, clinical, and biochemical findings.
       • Results:
         • Primary outcome: accuracy (based on AUC) significantly improved with PSMA PET-CT compared to conventional imaging (absolute difference: 27%, 92% PSMA PET-CT vs. 65% conventional imaging)
           • Sensitivity: 85% PSMA PET-CT vs. 38% conventional imaging
           • Specificity: 98% PSMA PET-CT vs. 91% conventional imaging
           • PSMA PET-CT more sensitive and specific than conventional imaging for both pelvic nodal or distant metastases
         • Secondary outcomes:
           • Change in management more common with PSMA PET-CT (28% PSMA PET-CT vs. 15% conventional imaging)
           • Less equivocal findings with PSMA PET-CT
           • Radiation exposure reduced with PSMA PET-CT (8 mSv PSMA PET-CT vs. 19 mSv conventional imaging)
       • Limitations:
         • Lack of histopathological evidence of metastasis in majority of cases; unclear validity of reference standard used in this study
           • Only 23% of positive cases (pelvic nodal or distant metastasis) met "hard" criteria to define metastasis (true positive).
             • Hard criteria were histopathology showing prostate adenocarcinoma, or change of a bone lesion to sclerotic or blastic on follow-up imaging.
       • Hofman, Michael S., et al. "Prostate-specific membrane antigen PET-CT in patients with high-risk prostate cancer before curative-intent surgery or radiotherapy (proPSMA): a prospective, randomised, multicentre study." The Lancet 395.10231 (2020): 1208-1216.
     • Clinical implications (2):
       1. PSMA PET/CT may identify nodes outside of the routine surgical field, as well as additional sites of distant disease
       2. Sensitivity of PSMA PET/CT in detecting nodal disease not high enough to avoid treatment of lymph nodes in patients with risk of lymph node involvement
2. Improved quantification of metastatic burden
   • Oligometastatic disease may be identified, and such patients may be offered management in clinical trials or metastasis-directed surgery.
3. Staging of biochemical recurrence
   • Most common indication for PSMA-targeted PET
   • Management of biochemical recurrence depends on disease extent: local recurrence of local recurrence with regional nodal metastases vs. distant metastatic disease
4. Determining patient suitability for PSMA-targeted radionuclide therapy
   • Both 177Lu and 225Ac PSMA-targeted radioligand therapy are emerging as promising therapies for castration-resistant disease.
5. Primary detection of tumor as an adjunct to multiparametric MRI
   • Role of PSMA-targeted PET as an adjunct to mpMRI for primary detection of clinically significant prostate cancer is not well-established

Indications

• FDA approved for (2)[48]
  1. To identify metastases, not demonstrated on conventional imaging, that are potentially curable by surgery or other therapy
  2. After biochemical recurrence, to evaluate for role of locoregional salvage treatment
• 2021 CUA Best Practice Report Recommendations for PSMA PET/CT[49]
  • PSMA-targeted PET may be helpful (3):
    1. To identify clinically significant prostate cancer when systematic biopsies and MRI are negative
       • Recommendation strength = 4 where "Strength of recommendation: 1=strong; 2=moderate; 3=weak."
    2. To identify metastases, not demonstrated on conventional imaging, that may influence management
       1. Primary staging of high-risk prostate cancer
       2. Castration-sensitive prostate cancer (confirm oligometastatic vs. extensive disease)
          • In metastatic, hormone-sensitive prostate cancer, docetaxel has level 1 evidence in males with high-volume disease, defined as visceral metastasis or ≥4 bone metastases with ≥ 1 beyond the vertebral bodies and pelvis
       3. Non-metastatic, castrate-resistant prostate cancer
          • If metastatic, consider systemic therapy
    3. After biochemical recurrence, to evaluate for role of locoregional salvage treatment
• Unknown if adoption of PSMA-PET resulting in improved staging of high-risk or after biochemical recurrence will result in improved overall survival.
  • Impact of PSMA-targeted PET on management ranged from 30–76%; modifications made to pre-PSMA-targeted PET planned management included avoidance of systemic therapy (19–50%) and PET-directed local therapy in up to 60% of cases[50]

Other

Risk calculators

• Concept: improve prediction models by combining variables
• Most widely used in prostate cancer: ERSPC and PCPT

Genetic testing

• Germline mutations are inherited from parents; all cells have the mutation except red blood cells
• Somatic mutations are acquired
• Indications
  • NCCN (version 2.2021)
    • Recommended (5)
      1. Metastatic (distant or regional (node-positive) prostate cancer
      2. High- or very-high risk localized prostate cancer
      3. Personal history of breast cancer
      4. Positive family history of high-risk germline mutations (e.g. BRCA 1/2, Lynch syndrome)
         • BRCA-cancers (5): breast, ovarian, pancreatic, prostate, melanoma
         • Lynch syndrome cancers: (8) colonic (most common), endometrial (second most common), prostate, urothelial, adrenal, gastric, pancreatic, uterine, ovarian, and sebaceous carcinomas
      5. Ashkenazi Jewish ancestry
    • Optional (2)
      1. Intermediate-risk with intraductal or cribiform histology
      2. Personal history of colorectal, gastric, melanoma, uppert tract urothelial, glioblastoma, biliary tract, or small intestine

Transrectal Ultrasound (TRUS) Biopsy

• Patients with clinical indications to confirm diagnosis of prostate cancer undergo TRUS biopy
• Triggers for biopsy
  • A PSA level that is considered suspicious for prostate cancer should be remeasured before performing a prostate biopsy because of fluctuations in PSA levels that could create false-positive elevations.
    • According to the AUA Choosing Wisely Campaign, empirical antibiotics should not be given to patients exclusively for an elevated PSA without any other urinary symptoms
  • The choice of a PSA threshold for recommending a prostate biopsy is controversial.
    • Historically, many would recommend prostate biopsy once a patient’s serum PSA level is >4.0 ng/mL. However, data from the Prostate Cancer Prevention Trial demonstrated an overall prostate cancer detection rate of 15% for all men with a PSA level < 4.0 ng/mL and nearly 15% having a Gleason score of 7 or greater, suggesting no absolute safe threshold.
  • Numerous organizations now recommend using PSA together with other methods of risk assessment, such as family history, race, DRE findings, and risk calculators

Questions

1. What is the function of PSA? What is the half life?
2. How does PSA circulate in the blood?
3. When does serum PSA become detectable?
4. What is the optimal MRI sequence to evaluate
   1. Hemorrhage
   2. Transition zone
   3. Vascularity of the prostate
   4. Peripheral zone
5. Describe the PROMIS and PRECISION trials
6. What is the differential diagnosis for an area of low signal intensity on T2WI?

Answers

1. What is the function of PSA? What is the half life?#*Liquify semen
   • 2-3 days
2. How does PSA circulate in the blood?
   • Circulates free (20-30%) and bound (70-80%).
   • Bound to 3 proteins: α1-antichymotripson, α2-macroglobulin, α1-protease inhibitor
3. When does serum PSA become detectable?
   • Puberty
4. What is the optimal MRI sequence to evaluate
   1. Hemorrhage
   2. Transition zone
   3. Vascularity of the prostate
   4. Peripheral zone
5. Describe the PROMIS and PRECISION trials
6. What is the differential diagnosis for an area of low signal intensity on T2WI?

References

• Wein AJ, Kavoussi LR, Partin AW, Peters CA (eds): CAMPBELL-WALSH UROLOGY, ed 11. Philadelphia, Elsevier, 2015, chap 108
• Wein AJ, Kavoussi LR, Partin AW, Peters CA (eds): CAMPBELL-WALSH UROLOGY, ed 11. Philadelphia, Elsevier, 2015, chap 111
• Balk, Steven P., Yoo-Joung Ko, and Glenn J. Bubley. "Biology of prostate-specific antigen." Journal of clinical oncology 21.2 (2003): 383-391.
• AUA Update Series (2016) Lesson 14: Multiparametric Magnetic Resonance Imaging for Prostate Cancer
• Shaygan, Bobby, et al. "Canadian Urological Association best practice report: Prostate-specific membrane antigen positron emission tomography/computed tomography (PSMA PET/CT) and PET/magnetic resonance (MR) in prostate cancer." Canadian Urological Association Journal 15.6 (2021): 162.