Track: Case Reports

Abstract:

Introduction: Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine tumor that recurs in approximately one-third of patients. The most common sites of metastasis are the lymph nodes, distant skin, liver, and bone. Only one patient has previously been documented to have metastatic disease to the heart.

Case: A 76-year-old patient was initially diagnosed with MCC of the left axilla in 2017 and treated with chemotherapy and radiation. The patient had recurrence in the left axilla and metastatic disease to the inguinal lymph nodes, lung, and pancreas for which he was placed on Avelumab intermittently since 2017. After Avelumab was held in December 2024, the patient developed chest pain and was found to have an epicardial mass between the right atrium and the ascending aorta. A biopsy of the epicardial mass was performed in May 2025 and revealed a high-grade neuroendocrine carcinoma that stained positive for synaptophysin, chromogranin, and cytokeratin CAM5.2, which occasionally showed a perinuclear dot-like pattern. INSM1 staining was variably positive and MCPyV staining was indeterminate. Stains for TTF-1, CK7, CK20, and p63 were negative. These findings were compatible with MCC. A PET scan in June 2025 demonstrated enlargement of the epicardial mass, and the patient was initiated on immunotherapy with plans to repeat imaging in three months.

Conclusion: Clinicians should be aware that MCC may metastasize to the heart.

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Noreen Mohsin