The role of PARP inhibitors in BRCA mutated pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) accounts for about 3% of all cancers in the United States and about 7% of all cancer deaths. Despite the lower prevalence relative to other solid tumors, it is one of the leading causes of cancer-related death in the US. PDAC is highly resistant to chemotherapy as well as radiation therapy. Current standard-of-care chemotherapeutic regimens provide transient disease control but eventually tumors develop chemoresistance. Tumors that are deficient in DNA damage repair mechanisms such as BRCA mutants respond better to platinum-based chemotherapies. However, these tumor cells can utilize the poly adenosine diphosphate (ADP)-ribose polymerase (PARP) as a salvage DNA repair pathway to prolong survival. Hence, in the presence of BRCA mutations, the inhibition of the PARP pathway can lead to tumor cell death. This provides the rationale for using PARP inhibitors in patients with BRCA mutated PDAC. The phase III POLO trial showed a near doubling of progression-free survival (PFS) compared with placebo in advanced PDAC when a PARP inhibitor, olaparib, was used as maintenance therapy. As a result, the US Food and Drug Administration (FDA) approved olaparib as a maintenance treatment for germline BRCA mutated advanced PDAC that has not progressed on platinum-based chemotherapy. The success of olaparib in treating advanced PDAC opened the new field for utilizing PARP inhibitors in patients with DNA damage repair (DDR) gene defects. Currently, many clinical trials with various PARP inhibitors are ongoing either as monotherapy or in combination with other agents. In addition to germline/somatic BRCA mutations, some trials are enrolling patients with defects in other DDR genes such as ATM, PALB2, and CHEK2. With many ongoing PARP inhibitor trials, it is hopeful that the management of PDAC will continuously evolve and eventually lead to improved patient outcomes.