Increasing Use of Conservative Management of Low-Risk Prostate Cancer in the Veterans Affairs System from 2012 to 2021

PURPOSE/OBJECTIVE(S)

Conservative management (CM), including either active surveillance or watchful waiting, is the preferred management strategy for men with low-risk prostate cancer. We sought to describe contemporary trends in CM among men with localized prostate cancer across the equal-access Veterans Affairs (VA) system.

MATERIALS/METHODS

Using VA tumor registry data, we identified all men with a new diagnosis of biopsy-proven, clinically node-negative, non-metastatic prostatic adenocarcinoma from 2012 to 2021, excluding men with missing National Comprehensive Cancer Network risk group. We quantified the yearly proportion of patients with low and favorable intermediate-risk (FIR) prostate cancer undergoing conservative management and examined age-specific rates. Multivariable logistic regression was used to identify independent clinical predictors of CM among men with low-risk and FIR disease.

RESULTS

The cohort included 86,415 patients with localized prostate cancer, of whom 20,290 (23.5%) had low risk and 25,447 (29.5%) had FIR disease. The proportion of men diagnosed with low-risk disease decreased from 27.7% in 2012 to 20.1% in 2021. The proportion of men with localized prostate cancer who were 70 years or older at diagnosis increased from 19.5% in 2012 to 46.4% in 2021, with similar increases seen across risk groups. The proportion of men with low-risk disease undergoing CM increased from 63.1% in 2012 to 86.6% in 2021. CM rates in 2021 among low-risk patients were largely consistent across age groups (50-59: 85.1%; 60-69: 87.4%; 70+: 86.3%). For FIR patients, CM rates increased among the subset with Gleason 6 disease (49.5% in 2012 to 80.7% in 2021). In multivariable models, independent predictors of CM in low-risk patients included older age, more recent year, lower PSA at diagnosis, North Atlantic or Pacific region, and presence of another cancer at diagnosis; similar predictors were found in FIR patients. Self-reported race (Black, White, or Other) was not associated with CM. While there was wide geographic variation in CM rates among low-risk patients early in the study period (2012-2014: 56.1% in Southeast region vs 74.1% in Pacific), these disparities resolved in recent years (2019-2021: 83.2% in Southeast vs 83.8% in Pacific).

CONCLUSION

Rates of conservative management for localized prostate cancer increased dramatically over time in the VA, with over 85% of low-risk patients managed conservatively in 2021. Recent years showed no differences in CM rates by self-reported race, geographic region, or age group. Despite this progress, we observed a concomitant increase in the proportion of men 70 years or older diagnosed with localized prostate cancer, including low risk disease. This raises a need to consider strategies to reduce the diagnosis of low-risk disease in elderly Veterans.

Success of Liquid Tumor Biopsy in Men with Metastatic Prostate Cancer According to Self-Identified Race

PURPOSE/OBJECTIVE(S)

Liquid biopsy using cell-free DNA (cfDNA) is increasingly used to identify somatic prostate cancer (PrCa) alterations when tissue biopsy of a metastatic lesion is infeasible or impractical. High-risk somatic alterations identified by cfDNA have been recently shown to predict the benefit of metastasis-directed therapy with stereotactic body radiation therapy in PrCa. However, given the older age of PrCa patients, liquid biopsy is often contaminated with alterations related to clonal hematopoiesis of indeterminate potential (CHIP), generating uncertainty in the clinical utility of the results. Given the higher incidence and aggressiveness of metastatic PrCa in Black men, we sought to determine if the success of cfDNA testing varied by race in a large and diverse cohort of United States Veterans with metastatic PrCa, hypothesizing that race would not influence the success of cfDNA testing.

MATERIALS/METHODS

Veterans with metastatic PrCa underwent next-generation sequencing of cfDNA biopsy specimens through the VA National Precision Oncology Program from February 2019 to November 2022. Successful identification of PrCa with cfDNA testing was defined as the identification of an alteration in one or more PrCa-related related genes in the gene panel tested (AR, CDK12, SPOP, MED12, CCND1, BRAF, AKT1, TMPRSS2, ERG, ETV1, and ETV4). Univariate logistic regression was employed to explore the association between patient self-identified race, as well as other patient and disease-specific factors at the time of cfDNA biopsy, with the likelihood of yielding a successful cfDNA biopsy result.

RESULTS

A total of 2066 cfDNA tests from 1985 Veterans were related to a diagnosis of PrCa, passed quality control measures, and were linkable to patient-level demographics. Median age at testing was 74, median PSA at testing was 22.7, median PSA doubling time (PSADT) was 3.6 months, and median Gleason score was 8. 57% of Veterans self-identified as White, 33% as Black, and 10% as Other. Eight hundred fourteen (39%) tests were deemed successful by finding a PrCa related gene alteration. Among successful tests, the most frequently encountered alterations were AR alterations in 60.4% White men and 33.9% Black men (p = 0.72), followed by TMPRSS2 alterations in 70.3% White men and 22.0% Black men (p<0.001). Despite a lower rate of PrCa-specific alterations in Black men, on univariate analysis, Veteran self-identified race was not associated with successful cfDNA testing (OR 0.95, 95% CI 0.78-1.14, p = 0.6), whereas PSA in quintiles 2-4, PSADT <12 months, and unit increase in Gleason score were associated with successful cfDNA testing (p<0.01 for all).

CONCLUSION

Successful cfDNA biopsy in metastatic PrCa is associated with PSA and PSADT, but not related to patient self-identified race. In appropriate clinical scenarios, patients who self-identify as Black or White are equally likely to have PrCa-specific alterations detected on cfDNA testing when evaluating metastatic PrCa patients for local and systemic therapies.

Epithelial stem cells of the prostate and their role in cancer progression

Prostate cancer is a leading cause of cancer-related death in adult men. It can regress dramatically upon antihormonal therapy, but it often recurs in a more aggressive, androgen-independent form. Defining the prostate tissue stem cells (PrSCs) and their involvement in cancer initiation and maintenance may lead to better therapeutics. Using a tissue-regeneration model in which dissociated prostate epithelial cells mixed with inductive mesenchyme give rise to prostatic tubules, we have identified a small population of prostate cells that contains multiple stem cell characteristics. In this system, prostate cancer can be initiated by autocrine or paracrine growth factor signaling and intracellular overexpression of genes often found mutated in human prostate cancer. Using an in vitro prostate sphere assay, we further defined the PrSC population and demonstrated their self-renewal and multilineage differentiation capabilities. Microarray analyses of the stem- and non-stem-cell populations have assisted us in finding and evaluating additional markers that can better define the PrSC population and further delineate the different cell types of the prostate, including those that serve as the target cell for tumor initiation.