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Rare Case Series Of 3 Patients With Metastatic Merkel Cell Carcinoma To The Pancreas And Response To Single Agent Immune Checkpoint Inhibitor
*Dennis Zambrano, *Luis I Ruffolo, *Eva Galka
University of Rochester, Rochester, NY

OBJECTIVE(S): Merkel cell carcinoma (MCC) is a rare primary cutaneous neuroendocrine neoplasm derived from the Merkel cell mechanoreceptors in the basal layer of the epidermis. Tumorigenesis is driven by Merkel Cell Polyomavirus (MCPyV) infection or cumulative UVB radiation exposure. Etiology is important because it may underlie clinical aggressiveness and subsequent response to immunotherapy. Here we present 3 patients with metastatic MCC to the pancreas, two of which had surgical resection with positive sentinel lymph nodes, and one who had pancreatic metastasis at presentation, all which responded to single agent checkpoint inhibitor (CPI).
METHODS: Retrospective review of all patients presenting to a tertiary referral center with a diagnosis of MCC was conducted. Patient characteristics, demographics, and clinicopathologic data was abstracted. Patient histories were reviewed for presence of distant metastases and location.
RESULTS: Between 2003-2018 112 patients presented for evaluation, 94 of which underwent wide local excision. Of these patients, 24 (25%) developed subsequent metastatic recurrence. Patients who developed metastases were more likely to have nodal positive disease at time of resection compared to those without recurrence (p=0.049). Of patients with metastatic disease, 3 had localized metastasis to the pancreas. Patient 1 and 2 presented with metastatic disease 10 and 16 months, respectively, after wide excision with positive SLNB and localized adjuvant radiation. Patient 3 presented with metastatic disease at onset. All patients experienced complete metabolic and near complete anatomic response to 4 cycles of pembrolizumab (Figure 1).
CONCLUSIONS: Metastatic MCC to the pancreas is a rare but potentially treatable condition with immunotherapy. Future work will focus on the intrinsic tumor factors that influence metastasis, such as MCPyV status. It has been shown that virus negative tumors express more neoantigens and elicit a stronger immune response, possibly explaining the favorable response to single agent CPI in the cases presented. Understanding the relationship between MCPyV and immune response may help guide adjuvant therapy in the future.


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