Phase II Study of Olaparib and Pembrolizumab in Advanced Melanoma With Homologous Recombination (HR) Mutation

Treatment with PARP inhibitors could represent a novel opportunity to selectively kill a subset of cancer cells with deficiencies in DNA repair pathways. For example, a tumor arising in a patient with a germline BRCA mutation (gBRCAmut) has a defective homologous recombination DNA repair pathway and would be increasingly dependent on NHEJ, alt-NHEJ, and BER for maintenance of genomic integrity. PARP inhibitors block alt-NHEJ and BER, forcing tumors with BRCA deficiencies to use the error-prone NHEJ to fix double-strand breaks. Non-BRCA deficiencies in homologous recombination DNA repair genes could also enhance tumor cell sensitivity to PARP inhibitors. The rationale for anticancer activity in a subset of non-gBRCAmut tumors is that they share distinctive DNA repair defects with gBRCAmut carriers, a phenomenon broadly described as "BRCAness." DNA repair defects can be caused by germline or somatic alterations to the homologous recombination DNA repair pathway. Homologous recombination is a complex pathway, and several genes other than BRCA1 and BRCA2 are required either to sense or repair DNA double-strand breaks via the homologous recombination pathway. Therefore, PARP inhibitors are also selectively cytotoxic for cancer cells with deficiencies in DNA repair proteins other than BRCA1 and BRCA2. In melanoma, genetic HR mutation/ alterations are rather common. Retrospective data showed that nearly 20-30% of cutaneous melanoma harbors a mutation in at least 1 of the HR genes in their tumor. The commonly altered genes were ARID1A, FANCA, ATM, BRCA1, ATRX and BRCA2, ATR, BRCA1 and BRIP1. These findings indicate that HR mutations / alterations are frequently observed in metastatic melanoma, and they suggest that PARP inhibitors could potentially be of a great clinical value in a substantial portion of the patients with advanced melanoma. In addition, the retrospective data also showed that presence of HR mutation was associated with high TMB and clinical response to checkpoint immunotherapy. Therefore, the investigators propose a phase II study of niraparib in patients with advanced melanoma with genetic homologous recombination mutation/ alteration. In this clinical study, clinical efficacy of olaparib in combination with pembrolizumab will be evaluated by assessing an objective clinical response rate in patients with advanced, metastatic melanoma with the homologous recombination (HR) pathway gene mutation / alteration. All participating patients will receive olaparib 300 mg a day and pembrolizumab 200 mg every 3 weeks (for up to 2 years) until disease progresses or they experience intolerable toxicity.