Abstract 817: Pancreatic acinar carcinoma - a rare entity with a targetable BRAF V600E mutation

Background: Pancreatic acinar carcinomas account for less than 1% of all pancreatic cancers and are considered genetically distinct entities form other pancreatic carcinomas. The pathogenesis of this malignancy is incompletely understood, and the efficacy of cytotoxic chemotherapy is not well defined especially in unresectable or metastatic disease. Methods: We identified one patient with pancreatic acinar carcinoma who was treated at our institution and was found to have a unique targetable pathogenic mutation on tumor sequencing. Results: A 64-year-old male patient was diagnosed with localized pancreatic acinar carcinoma during workup for epigastric pain. He underwent distal pancreatectomy with final pathology consistent with stage T3N0 acinar cell carcinoma without any adenocarcinoma component. He subsequently received six months of adjuvant chemotherapy with gemcitabine plus capecitabine, derived from evidence on pancreatic adenocarcinoma due to the size of his original tumor. Seven months after completion of adjuvant therapy, he was found to have local recurrence within the surgical bed and was treated with three cycles of systemic chemotherapy with FOLFIRINOX. During a following planned surgical resection, multiple liver lesions were seen intraoperatively, and surgery was aborted. Liver lesions were biopsied and hybrid capture next-generation sequencing was performed which revealed: a BRAF V600E gain of function mutation, CDKN2A loss as well as MYCN amplification. The patient declined further chemotherapy and his treatment was switched to Encorafenib (BRAF inhibitor) plus Binimetinib (MEK inhibitor). He attained a partial response to therapy at his first restaging CT scan after 2 months of therapy (-39% per RECIST 1.1). Both mass at the surgical bed as well as liver metastases were decreased in size. He tolerated treatment very well without significant adverse events (including no clinically significant rash). Conclusions: While BRAF rearrangements as described in the literature may occur in 15-23% of patients with acinar cell carcinoma of the pancreas, BRAF activating mutations and in particular the BRAF V600E substitution has not been reported. This particular substitution is commonly present in melanoma, hairy cell leukemia, Langerhans cell histiocytosis and less frequently in lung and colon cancer. A combination of BRAF and MEK inhibition may be used in patients with tumors harboring this activating mutation with variable efficacy across different histologies. In light of the rarity of acinar cell carcinomas of the pancreas and the lack of established systemic treatment guidelines, tumor sequencing should be considered if no other therapies are available. This is the first case reported in the literature of a patient with acinar cancer of the pancreas and BRAF V600E mutation where targeted therapy has shown an early response. Citation Format: Vaia Florou, Chris Nevala-Plagemann, Sean Mulvihill, Ignacio Garrido-Laguna. Pancreatic acinar carcinoma - a rare entity with a targetable BRAF V600E mutation [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 817.