A phase II study of maintenance rucaparib in patients with platinum sensitive, advanced pancreatic cancer and a pathogenic germline or somatic variant in BRCA1, BRCA2 or PALB2: A four year survival update.

Abstract

661 Background: We previously reported the results of a single arm, phase II study of maintenance rucaparib in patients with advanced, platinum-sensitive pancreatic cancer and pathogenic germline or somatic BRCA1, BRCA2 or PALB2 variants (Reiss et al, JCO, 2021). We now report the five year follow-up of this trial. Methods: Patients with advanced PC and a pathogenic germline or somatic variant in BRCA1, BRCA2 or PALB2 were enrolled in this single arm phase II study performed at the Abramson Cancer Center. Patients were required to have received ≥16 weeks of platinum-based treatment without evidence of platinum resistance, which was defined as growing lesions, new lesions or steadily rising tumor markers. Chemotherapy was discontinued and patients received rucaparib 600mg PO BID until progression or unacceptable toxicity. The primary endpoint was progression-free survival (PFS). Secondary endpoints included overall response rate (ORR), disease control rate (DCR) and overall survival (OS). Results: Of 42 evaluable patients, seven (16.7%) remain progression-free for over four years (5 gBRCA2, 1 sBRCA2, 1 gPALB2) of whom four (9.5%) have been progression-free for five years. Two of these four patients discontinued rucaparib due to adverse events after three and four years of therapy, respectively, without signs or symptoms of progression to date. At the cutoff date, we observe an mPFS 12.9 months, mOS 24.3 months, ORR 41.6% (9 PRs, 6 CRs), noting that three patients converted from partial to complete response since our prior publication. Two patients with ongoing responses succumbed to treatment-related MDS/AML following 2.1 and 4.8 years on study, respectively. Prior to receiving rucaparib, these individuals had received 13 and 10 months of cytotoxic chemotherapy for pancreatic cancer, respectively. Conclusions: Here we report the four year progression-free survival rate of maintenance rucaparib in patients with BRCA or PALB2 related pancreatic cancer. Our data suggest that a select portion of this patient population achieves highly durable clinical remissions. This finding is further highlighted by two patients who have discontinued rucaparib for adverse events one and two years ago, respectively, and have not had biochemical or imaging evidence of progression to date. Given the cost and risk of treatment-related leukemia associated with PARP inhibition, this data highlights the need to better understand the highly variable biology of patients with PC and BRCA or PALB2 variants, and raises the possibility of whether a very small, select group may be cured by PARP inhibitors. Clinical trial information: NCT03140670 .