Efficacy of systemic therapies in men with metastatic castration resistant prostate cancer harboring germline ATM versus BRCA2 mutations

Germline and somatic mutations in prostate cancer: Implications for treatment

Genetic testing is an integral part of the workup of metastatic prostate cancer, in part, because the results can have a profound impact on the subsequent management of this disease. There are now several Food & Drug Administration (FDA) approved therapeutics available for patients with prostate cancer and certain genetic abnormalities - most notably, mutations in DNA damage repair (DDR) pathways such mismatch repair (MMR) and homologous recombination repair (HRR). In this review of the current literature, we discuss the indications for somatic and germline testing, the genetic changes of particular clinical relevance, the associated therapeutic options, and the clinical data supporting their use. We also highlight select trials-in-progress and future directions for the field.

Poly (ADP-ribose) Polymerase Inhibitors Have Comparable Efficacy with Platinum Chemotherapy in Patients with BRCA-positive Metastatic Castration-resistant Prostate Cancer. A Systematic Review and Meta-analysis

CONTEXT

Testing for mutations in Breast Cancer Gene 1/2 (BRCA) has emerged as a novel decision-making tool for clinicians. Patients with metastatic castration-resistant prostate cancer (mCRPC) harboring pathogenic BRCA mutations can benefit from poly (ADP-ribose) polymerase inhibitor (PARPi) and platinum treatments, whereas the impact of the mutation on sensitivity to cabazitaxel and prostate-specific membrane antigen (PSMA)-ligand therapy is currently unknown.

OBJECTIVE

To assess the efficacy of PARPi, platinum, cabazitaxel, and PSMA-ligand therapies in BRCA-positive mCRPC.

EVIDENCE ACQUISITION

Databases were queried in February 2022. We performed data synthesis by using both proportional and individual patient data. For prostate-specific antigen (PSA) response rate (≥50% decrease from baseline [PSA50]) evaluation, we pooled event rates with 95% confidence intervals (CIs). Progression-free (PFS) and overall (OS) survival analyses with individual patient data were performed with the mixed-effect Cox proportional hazard model and single-arm random-effect analysis, providing pooled medians.

EVIDENCE SYNTHESIS

We included 23 eligible studies with 901 BRCA-positive mCRPC patients. PSA50 response rates for PARPi and platinum were 69% (CI: 53-82%), and 74% (CI: 49-90%), respectively. Analyses of OS data showed no difference between PARPi and platinum treatments (hazard ratio: 0.86; CI: 0.49-1.52; p = 0.6). The single-arm OS and PFS analyses revealed similarities among different PARPis; pooled PFS and OS medians were 9.7 mo (CI: 8.1-12.5) and 17.4 mo (CI: 12.7-20.1), respectively.

CONCLUSIONS

Our data revealed that different PARPis were similarly effective in terms of PFS and OS. Moreover, we found that PARPi and platinum therapy were comparable in terms of PSA50 response rate and OS, highlighting that platinum is a valid treatment option for BRCA-positive mCRPC patients. However, prospective interventional studies comparing these agents are essential to provide a higher level of evidence.

PATIENT SUMMARY

In this report, we found that different poly (ADP-ribose) polymerase inhibitors had similar efficacy, and platinum was a valid treatment option in BRCA-positive metastatic castration-resistant prostate cancer patients.

PARP Inhibitors in Metastatic Prostate Cancer: A Comprehensive Systematic Review and Meta-analysis of Existing Evidence

Poly (ADP-ribose) polymerase inhibitors (PARPi) represent an option in selected cases of metastatic castration-resistant prostate cancer (mCRPC). The aim of the present systematic review and meta-analysis is to evaluate the efficacy and safety of approved (Olaparib, Rucaparib) and investigational (Talazoparib, Niraparib, Veliparib) PARPi in mCRPC patients. Three databases were queried for studies analyzing oncological outcomes and adverse events of mCRPC patients receiving PARPi. Primary outcome was a PSA decline ≥ 50% from baseline. Secondary outcomes were objective response rate, progression-free survival (PFS), radiological PFS, overall survival (OS), conversion of circulating tumor cell count, and time to PSA progression. The number and rate of any grade adverse events (AEs), grade ≥ 3 AEs, and most common grade ≥ 3 AEs were registered. A subanalysis of outcomes per mutation type, prospective trials, and studies adopting combination therapies was performed. Overall, 31 studies were included in this systematic review, 28 of which are available for meta-analysis. The most frequently investigated drug was Olaparib. The most frequent mutation was BRCA2. A PSA decline rate of 43% (95% CI 0.32-0.54) was observed in the overall population. Mean OS was 15.9 (95% CI 12.9-19.0) months. In BRCA2 patients, PSA decline rate was 66% (95% CI 0.57-0.7) and OS 23.4 months (95% CI 22.8-24.1). Half of the patients suffered from grade 3 and 4 AEs (0.50 [95% CI 0.39-0.60]). Most common AEs were hematological, the most frequent being anemia (21.5%). PARP inhibitors represent a viable option for mCRPC patients. Current evidence suggests an increased effectiveness in homologous recombination repair (HRR) gene mutation carriers, especially BRCA2.

Therapeutic sensitivity to standard treatments in BRCA positive metastatic castration-resistant prostate cancer patients-a systematic review and meta-analysis

BACKGROUND

Recent oncology guidelines recommend BRCA1/2 testing for a wide range of prostate cancer (PCa) patients. In addition, PARP inhibitors are available for mutation-positive metastatic castration-resistant PCa (mCRPC) patients following prior treatment with abiraterone, enzalutamide or docetaxel. However, the question of which of these standard treatments is the most effective for BRCA1/2 positive mCRPC patients remains to be answered. The aim of this meta-analysis was to assess the efficacy of abiraterone, enzalutamide and docetaxel in BRCA1/2 mutation-positive mCRPC patients in terms of PSA-response (PSA50), progression-free survival (PFS) and overall survival (OS).

METHODS

As no interventional trials are available on this topic, we performed the data synthesis of BRCA1/2 positive mCRPC patients by using both proportional and individual patient data. For PSA50 evaluation, we pooled event rates with 95% confidence intervals (CI), while for time-to-event (PFS, OS) analyses we used individual patient data with random effect Cox regression calculations.

RESULTS

Our meta-analysis included 16 eligible studies with 348 BRCA1/2 positive mCRPC patients. In the first treatment line, response rates for abiraterone, enzalutamide and docetaxel were 52% (CI: 25-79%), 64% (CI: 43-80%) and 55% (CI: 36-73%), respectively. Analyses of individual patient data revealed a PFS (HR: 0.47, CI: 0.26-0.83, p = 0.010) but no OS (HR: 1.41, CI: 0.82-2.42, p = 0.210) benefit for enzalutamide compared to abiraterone-treated patients.

CONCLUSIONS

Our PSA50 analyses revealed that all the three first-line treatments have therapeutic effect in BRCA1/2 positive mCRPC; although, based on the results of PSA50 and PFS analyses, BRCA positive mCRPC patients might better respond to enzalutamide treatment. However, molecular marker-driven interventional studies directly comparing these agents are crucial for providing higher-level evidence.

Metastatic Prostate Cancers with BRCA2 versus ATM Mutations Exhibit Divergent Molecular Features and Clinical Outcomes

PURPOSE

In patients with metastatic prostate cancer (mPC), ATM and BRCA2 mutations dictate differences in PARPi inhibitor response and other therapies. We interrogated the molecular features of ATM- and BRCA2-mutated mPC to explain the divergent clinical outcomes and inform future treatment decisions.

EXPERIMENTAL DESIGN

We examined a novel set of 1,187 mPCs after excluding microsatellite-instable (MSI) tumors. We stratified these based on ATM (n = 88) or BRCA2 (n = 98) mutations. As control groups, mPCs with mutations in 12 other homologous recombination repair (HRR) genes were considered non-BRCA2/ATM HRR-deficient (HRDother, n = 193), whereas lack of any HRR mutations were considered HRR-proficient (HRP; n = 808). Gene expression analyses were performed using Limma. Real-world overall survival was determined from insurance claims data.

RESULTS

In noncastrate mPCs, only BRCA2-mutated mPCs exhibited worse clinical outcomes to AR-targeted therapies. In castrate mPCs, both ATM and BRCA2 mutations exhibited worse clinical outcomes to AR-targeted therapies. ATM-mutated mPCs had reduced TP53 mutations and harbored coamplification of 11q13 genes, including CCND1 and genes in the FGF family. BRCA2-mutated tumors showed elevated genomic loss-of-heterozygosity scores and were often tumor mutational burden high. BRCA2-mutated mPCs had upregulation of cell-cycle genes and were enriched in cell-cycle signaling programs. This was distinct from ATM-mutated tumors.

CONCLUSIONS

Tumoral ATM and BRCA2 mutations are associated with differential clinical outcomes when patients are stratified by treatments, including hormonal or taxane therapies. ATM- and BRCA2-mutated tumors exhibited differences in co-occurring molecular features. These unique molecular features may inform therapeutic decisions and development of novel therapies.

Positive response to niraparib in chemo-refractory patients with metastatic appendiceal mucinous adenocarcinoma harboring ATM mutations: A case report

Background

Appendiceal mucinous adenocarcinoma, one kind of specific colorectal cancer, is lowly prevalent and rarely diagnosed in clinical practice. In addition, there have been limited standard treatment strategies established for patients with appendiceal mucinous adenocarcinoma, especially with metastatic disease. The regimens for colorectal cancer, which were adopted in appendiceal mucinous adenocarcinoma, usually resulted in limited effectiveness.

Case presentation

Herein, we presented a case of chemo-refractory patient with metastatic appendiceal mucinous adenocarcinoma harboring ATM pathological mutation of exon 60, c.8734del, p.R2912Efs*26, and who has achieved a persistent response to salvage treatment of niraparib, with disease control time that reached 17 months and still in extension.

Conclusions

We supposed that appendiceal mucinous adenocarcinoma patients harboring ATM pathological mutations may respond to the treatment of niraparib, even without a homologous recombination deficiency (HRD) status; however, it needs further confirmation in a larger cohort.

Differential responses to taxanes and PARP inhibitors in ATM- versus BRCA2-mutated metastatic castrate-resistant prostate cancer

BACKGROUND

PARP (poly(ADP-ribose) polymerase) inhibitors (PARPi) are now standard of care in metastatic castrate-resistant prostate cancer (mCRPC) patients with select mutations in DNA damage repair (DDR) pathways, but patients with ATM- and BRCA2 mutations may respond differently to PARPi. We hypothesized that differences may also exist in response to taxanes, which may inform treatment sequencing decisions.

METHODS

mCRPC patients (N = 158) with deleterious ATM or BRCA2 mutations who received taxanes, PARPi, or both were retrospectively identified from 11 US academic centers. Demographic, treatment, and survival data were collected. Kaplan-Meier analyses were performed and Cox hazard ratios (HR) were calculated for progression-free survival (PFS) as well as overall survival (OS), from time of first taxane or PARPi therapy.

RESULTS

Fifty-eight patients with ATM mutations and 100 with BRCA2 mutations were identified. Fourty-four (76%) patients with ATM mutations received taxane only or taxane before PARPi, while 14 (24%) received PARPi only or PARPi before taxane. Patients with ATM mutations had longer PFS when taxane was given first versus PARPi given first (HR: 0.74 [95% confidence interval [CI]: 0.37-1.50]; p = 0.40). Similarly, OS was longer in patients with ATM mutations who received taxane first (HR: 0.56 [CI: 0.20-1.54]; p = 0.26). Among patients with BRCA2 mutations, 51 (51%) received taxane first and 49 (49%) received PARPi first. In contrast, patients with BRCA2 mutations had longer PFS when PARPi was given first versus taxane given first (HR: 0.85 [CI: 0.54-1.35]; p = 0.49). Similarly, OS was longer in patients with BRCA2 mutations who received PARPi first (HR: 0.75 [CI: 0.41-1.37]; p = 0.35).

CONCLUSIONS

Our retrospective data suggest differential response between ATM and BRCA2 mutated prostate cancers in terms of response to PARPi and to taxane chemotherapy. When considering the sequence of PARPi versus taxane chemotherapy for mCRPC with DDR mutations, ATM, and BRCA2 mutation status may be helpful in guiding choice of initial therapy.

Prognostic significance of pathogenic variants in BRCA1, BRCA2, ATM and PALB2 genes in men undergoing hormonal therapy for advanced prostate cancer

BACKGROUND

The prognostic significance of germline variants in homologous recombination repair genes in advanced prostate cancer (PCa), especially with regard to hormonal therapy, remains controversial.

METHODS

Germline DNA from 549 Japanese men with metastatic and/or castration-resistant PCa was sequenced for 27 cancer-predisposing genes. The associations between pathogenic variants and clinical outcomes were examined. Further, for comparison, DNA from prostate biopsy tissue samples from 80 independent patients with metastatic PCa were analysed.

RESULTS

Forty-four (8%) patients carried germline pathogenic variants in one of the analysed genes. BRCA2 was most frequently altered (n = 19), followed by HOXB13 (n = 9), PALB2 (n = 5) and ATM (n = 5). Further, the BRCA1, BRCA2, PALB2 and ATM variants showed significant association with a short time to castration resistance and overall survival (hazard ratio = 1.99 and 2.36; 95% CI, 1.15-3.44 and 1.23-4.51, respectively), independent of other clinical variables. Based on log-rank tests, the time to castration resistance was also significantly short in patients with BRCA1, BRCA2, PALB2 or ATM somatic mutations and TP53 mutations.

CONCLUSIONS

Germline variants in BRCA1, BRCA2, PALB2 or ATM are independent prognostic factors of the short duration of response to hormonal therapy in advanced PCa.

The growing role of rucaparib in contemporary treatment of metastatic prostate cancer: a review of efficacy and guidance for side effect management

INTRODUCTION

In May 2020, the approval of rucaparib - a poly-ADP-ribose polymerase (PARP) inhibitor - in the USA marked the arrival of a new class of targeted therapeutics for a subset of metastatic castration-resistant prostate cancer patients whose tumors harbor germline or somatic BRCA1/2 gene alterations. It has now become critical for physicians to be aware of the role and nuances of management of PARP inhibitor therapies in prostate cancer.

AREAS COVERED

We focus on rucaparib's pharmacology, key clinical trials that support its current indication, the competitive landscape, and our considerations for management of adverse events. We also review the ongoing clinical trials that may expand its utility in prostate cancer in our expert opinion. Finally, we discuss the opportunities that exist for further development of this class of targeted agents in prostate cancer.

EXPERT OPINION

We believe that the time has come to develop functional assays of HRR proficiency or deficiency in order to better guide PARP inhibitor selection for patients with prostate cancer and beyond.

Implications of DNA damage repair alterations for the management of prostate cancer

PURPOSE OF REVIEW

In this review, we summarize the prevalence of alterations in DNA damage repair (DDR) genes in prostate cancer, their clinical significance, the therapeutic strategies developed to take advantage of the impaired tumour ability to repair DNA and the diagnostic approaches available to identify patients likely to benefit from DDR-targeting agents.

RECENT FINDINGS

DDR alterations are more frequent in metastatic than in localized prostate cancer and some of them associate with aggressive disease whereas the significance of others remain unclear. The most appropriate management approach for DDR-defective prostate cancer patients is unknown. Clinical trials have demonstrated the efficacy of different poly-ADP ribose polymerase inhibitors (PARPi) to treat metastatic castration-resistant prostate cancer patients with BRCA1/2 alterations, although there may be other DDR alterations that sensitize patients to these drugs. Multiple strategies to target DDR defects are being investigated, including PARPi in combination, platinum-based chemotherapy and immunotherapy, both in earlier and late disease stages. Optimization of molecular testing is paramount for the implementation of precision oncology in prostate cancer.

SUMMARY

Certain DDR defects present in prostate cancer have prognostic and therapeutic implications whereas the significance of other DDR alterations is yet to be elucidated.

The role of genetic testing in prostate cancer screening, diagnosis, and treatment

PURPOSE OF REVIEW

This review provides an overview of the current role of genetic testing in prostate cancer screening, diagnosis, and treatment.

RECENT FINDINGS

Recent studies have uncovered few but highly penetrant rare pathogenic mutations (RPMs), in genes, such as BRCA2, with strong prostate cancer risk and outcomes associations. Over 260 single nucleotide polymorphisms (SNPs) have also been identified, each associated with small incremental prostate cancer risk and when combined in a polygenic risk score (PRS), they provide strong prostate cancer risk prediction but do not seem to predict outcomes. Tumor tissue sequencing can also help identify actionable somatic mutations in many patients with advanced prostate cancer and inform on their risk of harboring a germline pathogenic mutation.

SUMMARY

RPM testing, PRS testing, and tumor sequencing all have current and/or potential future roles in personalized prostate cancer care.