Background: High-fidelity repair of DNA damage repair (DDR) (either single-strand- [SSBs] or double-strand breaks [DSBs]) is necessary for maintaining genomic integrity and cell survival. DDR alterations are commonly found in genitourinary malignancies involving either DSB repair by the homologous recombination (HR) repair (HRR) system (BRCA1/2 pathway) or the SSB repair through the poly (ADP-ribose) polymerase (PARP) pathway. PARP inhibitors (PARPi) exploit defects in the DNA repair pathway through synthetic lethality, DSBs being repaired only in HR-proficient cells but not in HR-deficient (HRD) cells.
Summary: A growing body of evidence supports the need for identification of germinal and somatic DDR alterations in patients with genitourinary malignancies. PARPi have already shown significant survival benefits in patients harboring HRR mutations in advanced settings, paving the way for precision medicine.
Key messages: In advanced prostate cancer (PCa), somatic mutations in HRR pathway are observed in up to 27% of metastatic resistant-to-castration PCa (mCRPC), although occurring early in PCa development, and mainly involving BRCA2, ATM, CHEK2, and BRCA1. Overall, germinal alterations are present in roughly 30-50% of cases of HRR alterations, and relative risk of PCa in germinal BRCA2 alteration carriers is 4.65-fold higher compared to noncarriers. Determination of DDR gene status is recommended in metastatic patients, a fortiori in mCRPC setting, since it could be a putative biomarker of response to first line of treatment (androgen-receptor signaling inhibitors [ARSI] vs. taxane-based chemotherapy) and allows to assess eligibility for PARPi use. Thus, olaparib (combined with androgen deprivation therapy) recently improved overall survival in mCRPC HRD patients, after new hormonal therapy (NHT) and led to its approvement for patients with an alteration in 14 of 15 prespecified HRR genes. Moreover, since preclinical data suggested synergic action between PARPi and ARSI, the use of either olaparib or niraparib has also been proposed in combination with NHT, with a radiological progression-free survival improvement when used with abiraterone. In urothelial carcinoma, a DDR gene alteration is identified in 23-54% of patients mostly in muscle-invasive bladder cancer, with a strong association between DDR gene mutation and a higher tumor mutation burden and sensitivity to cisplatin-based chemotherapy and immunotherapy. Recent phase 2 trials supported the use of HRR status to select patients for PARPi treatment in advanced urothelial carcinoma. Finally, in renal cell carcinomas (RCCs), pathogenic germline variants in DDR genes were identified in 7.3% of the cases, and deleterious somatic alterations have also been described as recurrent genomic events in patients with advanced RCC.
Keywords: BRCA2; DNA damage repair; Germinal/somatic mutation; Prostate cancer; Urothelial carcinoma.
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