Management and Prognosis of Cardiac Metastatic Merkel Cell Carcinoma: A Case–Control Study and Literature Review

SIMPLE SUMMARY: Approximately 20% of patients with Merkel cell carcinoma (MCC) will develop distant metastasis. Rarely, MCC metastases may involve the heart; there are limited data on management and prognosis of cardiac metastasis of MCC. Among a prospective registry of 582 patients with metastatic MCC (mMCC), we identified 9 patients (1.5%) with cardiac involvement. We found that cardiac mMCC most commonly involves the right heart (8 of 9; 89%) and occurs relatively late in the disease process (median 925 days from the initial diagnosis to cardiac involvement). In our cohort, cardiac mMCC frequently responds to immunotherapy and cardiac radiotherapy, which can both be delivered with minimal cardiac toxicity. Cardiac involvement was not associated with worse survival compared to MCC patients with non-cardiac distant disease. These results are timely as cardiac mMCC may be increasingly encountered in the era of immunotherapy as patients with metastatic MCC live longer. ABSTRACT: Merkel cell carcinoma (MCC), an aggressive neuroendocrine skin cancer, has a high rate (20%) of distant metastasis. Within a prospective registry of 582 patients with metastatic MCC (mMCC) diagnosed between 2003–2021, we identified 9 (1.5%) patients who developed cardiac metastatic MCC (mMCC). We compared overall survival (OS) between patients with cardiac and non-cardiac metastases in a matched case–control study. Cardiac metastasis was a late event (median 925 days from initial MCC diagnosis). The right heart was predominantly involved (8 of 9; 89%). Among 7 patients treated with immunotherapy, 6 achieved a complete or partial response of the cardiac lesion. Among these 6 responders, 5 received concurrent cardiac radiotherapy (median 20 Gray) with immunotherapy; 4 of 5 did not have local disease progression or recurrence in the treated cardiac lesion. One-year OS was 44%, which was not significantly different from non-cardiac mMCC patients (45%, p = 0.96). Though it occurs relatively late in the disease course, cardiac mMCC responded to immunotherapy and/or radiotherapy and was not associated with worse prognosis compared to mMCC at other anatomic sites. These results are timely as cardiac mMCC may be increasingly encountered in the era of immunotherapy as patients with metastatic MCC live longer.