ABSTRACT
BACKGROUND: Prostate-specific membrane antigen (PSMA) is a rational target for noninvasive detection of recurrent prostate cancer (PCa) and for therapy of metastatic castration-resistant prostate cancer (mCRPC) with PSMA-targeted agents. Here we conducted serial measurements of PSMA expression on circulating tumor cells (CTCs) to evaluate patterns of longitudinal PSMA dynamics over the course of multiple sequential therapies. METHODS: A retrospective investigation of men with mCRPC undergoing evaluation at medical oncology clinics at our institution assessed the dynamics of PSMA expression in the context of different systemic treatments administered sequentially. Eligibility included patients who began systemic therapies with androgen receptor (AR)-directed agents or taxane agents for whom peripheral blood samples were tested for CTC mRNA of AR splice variant-7 (AR-V7), prostate-specific antigen (PSA), and PSMA (with >2 CTC + results) in a CLIA-accredited laboratory. RESULTS: From August 2015 to November 2017, we identified 96 eligible men. Fifteen had greater than or equal to 2 sequential therapies and evaluable CTC samples, greater than or equal to 1 expressing PSMA (PSMA+). Among the 15 patients included in this analysis, a total of 54 PSMA status evaluations were performed in the context of 48 therapies during a median follow-up of 18 months. At baseline, PSMA signal was detected ("positive") in 11 of 15 (73.3%) patients, while for 4 of 15 (26.7%) patients PSMA signal was undetectable ("negative"). In all but two patients, the baseline collection corresponded with a change in treatment. On the second assessment, PSMA increases were detected in all 4/4 (100%) PSMA-negative patients and 8 of 11 (72.7%) PSMA-positive patients. PSMA significantly decreased in a patient treated with 177 Lu-PSMA-617. Serum PSA declines were seen in 7 of 8 (88%) of the treatment periods where PSMA decreased. CONCLUSIONS: PSMA expression in CTCs is a dynamic marker. PSMA transcript declines appear to be associated with concurrent decreases in serum PSA. Sequential CTC sampling could provide a noninvasive response assessment to systemic treatment for mCRPC.
Subject(s)
Antigens, Surface/blood , Glutamate Carboxypeptidase II/blood , Neoplasm Recurrence, Local/therapy , Neoplastic Cells, Circulating/chemistry , Prostatic Neoplasms, Castration-Resistant/therapy , Prostatic Neoplasms/blood , Prostatic Neoplasms/therapy , Aged , Aged, 80 and over , Antigens, Surface/genetics , Bridged-Ring Compounds/therapeutic use , Dipeptides/therapeutic use , Glutamate Carboxypeptidase II/genetics , Heterocyclic Compounds, 1-Ring/therapeutic use , Humans , Lutetium , Male , Middle Aged , Neoplasm Recurrence, Local/blood , Pilot Projects , Prostate-Specific Antigen/blood , Prostate-Specific Antigen/genetics , Prostatic Neoplasms, Castration-Resistant/blood , RNA, Messenger/blood , Receptors, Androgen/drug effects , Retrospective Studies , Taxoids/therapeutic use , Treatment OutcomeABSTRACT
BACKGROUND: Inherited DNA-repair gene mutations are more prevalent in men with advanced prostate cancer than previously thought, but their clinical implications are not fully understood. OBJECTIVE: To investigate the clinical significance of germline DNA-repair gene alterations in men with metastatic castration-resistant prostate cancer (mCRPC) receiving next-generation hormonal therapy (NHT), with a particular emphasis on BRCA/ATM mutations. DESIGN, SETTING, AND PARTICIPANTS: We interrogated 50 genes for pathogenic or likely pathogenic germline mutations using leukocyte DNA from 172 mCRPC patients beginning treatment with first-line NHT with abiraterone or enzalutamide. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: We assessed the impact of germline DNA-repair gene mutation status on ≥50% and ≥90% PSA responses, PSA progression-free survival (PSA-PFS), clinical/radiologic progression-free survival (PFS), and overall survival (OS). Survival outcomes were adjusted using propensity score-weighted multivariable Cox regression analyses. RESULTS AND LIMITATIONS: Among 172 mCRPC patients included, germline mutations (in any DNA-repair gene) were found in 12% (22/172) of men, and germline BRCA/ATM mutations specifically in 5% (9/172) of men. In unadjusted analyses, outcomes to first-line NHT were better in men with germline BRCA/ATM mutations (vs no mutations) with respect to PSA-PFS (hazard ratio [HR] 0.47; p=0.061), PFS (HR 0.50; p=0.090), and OS (HR 0.28; p=0.059). In propensity score-weighted multivariable analyses, outcomes were superior in men with germline BRCA/ATM mutations with respect to PSA-PFS (HR 0.48, 95% confidence interval [CI] 0.25-0.92; p=0.027), PFS (HR 0.52, 95% CI 0.28-0.98; p=0.044), and OS (HR 0.34, 95% CI 0.12-0.99; p=0.048), but not in men with non-BRCA/ATM germline mutations (all p>0.10). These results require prospective validation, and our conclusions are limited by the small number of patients (n=9) with BRCA/ATM mutations. CONCLUSIONS: Outcomes to first-line NHT appear better in mCRPC patients harboring germline BRCA/ATM mutations (vs no mutations), but not for patients with other non-BRCA/ATM germline mutations. PATIENT SUMMARY: Patients with metastatic castration-resistant prostate cancer and harboring germline mutations in BRCA1/2 and ATM benefit from treatment with abiraterone and enzalutamide.