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.