Practice patterns related to prostate cancer grading: results of a 2019 Genitourinary Pathology Society clinician survey

Contemporary Diagnostic Reporting for Prostatic Adenocarcinoma: Morphologic Aspects, Molecular Correlates, and Management Perspectives

The diagnosis and reporting of prostatic adenocarcinoma have evolved from the classic framework promulgated by Dr Donald Gleason in the 1960s into a complex and nuanced system of grading and reporting that nonetheless retains the essence of his remarkable observations. The criteria for the "Gleason patterns" originally proposed have been continually refined by consensuses in the field, and Gleason scores have been stratified into a patient-friendly set of prognostically validated and widely adopted Grade Groups. One product of this successful grading approach has been the opportunity for pathologists to report diagnoses that signal carefully personalized management, placing the surgical pathologist's interpretation at the center of patient care. At one end of the continuum of disease aggressiveness, personalized diagnostic care means to sub-stratify patients with more indolent disease for active surveillance, while at the other end of the continuum, reporting histologic markers signaling aggression allows sub-stratification of clinically significant disease. Whether contemporary reporting parameters represent deeper nuances of more established ones (eg, new criteria and/or quantitation of Gleason patterns 4 and 5) or represent additional features reported alongside grade (intraductal carcinoma, cribriform patterns of carcinoma), assessment and grading have become more complex and demanding. Herein, we explore these newer reporting parameters, highlighting the state of knowledge regarding morphologic, molecular, and management aspects. Emphasis is made on the increasing value and stakes of histopathologists' interpretations and reporting into current clinical risk stratification and treatment guidelines.

Does Overgrading on Targeted Biopsy of Magnetic Resonance Imaging-visible Lesions in Prostate Cancer Lead to Overtreatment?

BACKGROUND AND OBJECTIVE

Targeted biopsy of the index prostate cancer (PCa) lesion on multiparametric magnetic resonance imaging (MRI) is effective in reducing the risk of overdiagnosis of indolent PCa. However, it remains to be determined whether MRI-targeted biopsy can lead to a stage shift via overgrading of the index lesion by focusing only on the highest-grade component, and to a subsequent risk of overtreatment. Our aim was to assess whether overgrading on MRI-targeted biopsy may lead to overtreatment, using radical prostatectomy (RP) specimens as the reference standard.

METHODS

Patients with clinically localized PCa who had positive MRI findings (Prostate Imaging-Reporting and Data System [PI-RADS] score ≥3) and Gleason grade group (GG) ≥2 disease detected on MRI-targeted biopsy were retrospectively identified from a prospectively maintained database that records all RP procedures from eight referral centers. Biopsy grade was defined as the highest grade detected. Downgrading was defined as lower GG for the RP specimen than for MRI-targeted biopsy. Overtreatment was defined as downgrading to RP GG 1 for cases with GG ≥2 on biopsy, or to RP low-burden GG 2 for cases with GG ≥3 on biopsy.

KEY FINDINGS AND LIMITATIONS

We included 1020 consecutive biopsy-naïve patients with GG ≥2 PCa on MRI-targeted biopsy in the study. Pathological analysis of RP specimens showed downgrading in 178 patients (17%). The transperineal biopsy route was significantly associated with a lower risk of downgrading (odds ratio 0.364, 95% confidence interval 0.142-0.814; p = 0.022). Among 555 patients with GG 2 on targeted biopsy, only 18 (3.2%) were downgraded to GG 1 on RP. Among 465 patients with GG ≥3 on targeted biopsy, three (0.6%) were downgraded to GG 1 and seven were downgraded to low-burden GG 2 on RP. The overall risk of overtreatment due to targeted biopsy was 2.7% (28/1020).

CONCLUSIONS AND CLINICAL IMPLICATIONS

Our multicenter study revealed no strong evidence that targeted biopsy results could lead to a high risk of overtreatment.

PATIENT SUMMARY

In the diagnosis pathway for prostate cancer, results for targeted biopsies guided by magnetic resonance imaging (MRI) scans lead to a negligible proportion of overtreatment.

Prostate magnetic resonance imaging-targeted biopsy global grade correlates better than highest grade with prostatectomy grade

BACKGROUND

Magnetic resonance imaging (MRI)-targeted prostate biopsy has become an increasingly common method of diagnosing prostate cancer. A previous study from our institution demonstrated that the biopsy global Grade Group (gGG, aggregate GG of all positive cores) and highest Grade Group (hGG in any core) both show substantial concordance with the Grade Group at radical prostatectomy (RPGG) while the discordance predominantly consists of upgrading in gGG and downgrading in hGG. We performed a larger cohort study focused on biopsy cases in which gGG and hGG differ, to determine their relative concordance with RPGG.

METHODS

We conducted a retrospective review of radical prostatectomy specimens with prior MRI-targeted biopsies from our institution between 2016 and 2020. Separate gGG and hGG were assigned to each MRI-targeted lesion. Targeted lesions with different gGG versus hGG were segregated from those with identical gGG and hGG. The concordance of biopsy GG with RPGG was evaluated using κ coefficient analysis.

RESULTS

Of the 489 lesions with MRI-targeted biopsies, 82 (17%) differed in gGG versus hGG. The gGG of 46 (56%), 33 (40%), and 3 (4%) lesions were unchanged, upgraded, and downgraded at radical prostatectomy, respectively (κ= 0.302, weighted κ = 0.334). The hGG of 24 (29%), 9 (11%), and 49 (60%) lesions were unchanged, upgraded, and downgraded at radical prostatectomy, respectively (κ = 0.040, weighted κ = 0.198). When stratified by the biopsy GG, gGG showed the highest concordance in GG2 (61%) and GG3 (54%) lesions. The hGG resulted in substantial downgrading (60%) with less optimal concordance regardless of the biopsy GG. Neither the prebiopsy prostate specific antigen level nor the PI-RADS score was predictive of upgrading of gGG.

CONCLUSIONS

When gGG and hGG differ, gGG method more accurately predicts the RPGG than hGG, particularly in GG2 and GG3 lesions which comprised the majority of targeted lesions.

A distinct repertoire of cancer-associated fibroblasts is enriched in cribriform prostate cancer

Outcomes for men with localized prostate cancer vary widely, with some men effectively managed without treatment on active surveillance, while other men rapidly progress to metastatic disease despite curative-intent therapies. One of the strongest prognostic indicators of outcome is grade groups based on the Gleason grading system. Gleason grade 4 prostate cancer with cribriform morphology is associated with adverse outcomes and can be utilized clinically to improve risk stratification. The underpinnings of disease aggressiveness associated with cribriform architecture are not fully understood. Most studies have focused on genetic and molecular alterations in cribriform tumor cells; however, less is known about the tumor microenvironment in cribriform prostate cancer. Cancer-associated fibroblasts (CAFs) are a heterogeneous population of fibroblasts in the tumor microenvironment that impact cancer aggressiveness. The overall goal of this study was to determine if cribriform prostate cancers are associated with a unique repertoire of CAFs. Radical prostatectomy whole-tissue sections were analyzed for the expression of fibroblast markers (ASPN in combination with FAP, THY1, ENG, NT5E, TNC, and PDGFRβ) in stroma adjacent to benign glands and in Gleason grade 3, Gleason grade 4 cribriform, and Gleason grade 4 noncribriform prostate cancer by RNAscope®. Halo® Software was used to quantify percent positive stromal cells and expression per positive cell. The fibroblast subtypes enriched in prostate cancer were highly heterogeneous. Both overlapping and distinct populations of low abundant fibroblast subtypes in benign prostate stroma were enriched in Gleason grade 4 prostate cancer with cribriform morphology compared to Gleason grade 4 prostate cancer with noncribriform morphology and Gleason grade 3 prostate cancer. In addition, gene expression was distinctly altered in CAF subtypes adjacent to cribriform prostate cancer. Overall, these studies suggest that cribriform prostate cancer has a unique tumor microenvironment that may distinguish it from other Gleason grade 4 morphologies and lower Gleason grades.