Merkel Cell Carcinoma Presenting as a Malignant Pleural Effusion Post-COVID-19 Hospitalization: a Case Report and Literature Review

Abstract Introduction/Objective Merkel cell carcinoma (MCC) is a rare, highly aggressive neuroendocrine of the skin, associated with immunosuppression, UV light exposure, and polyomavirus (MCPyV). Metastatic MCC diagnosed in body fluid cytology extremely rare. Here, we report on case 65-year-old male presenting right pleural effusion remote history MCC, unknown to us during cytologic evaluation effusion. To best our knowledge, this sixth metastatic reported English literature, first one patient previously admitted for COVID-19 pneumonia. Methods/Case Report A presented dyspnea acute hypoxic respiratory failure. Past medical was significant squamous forearm excised four months prior ulcerative colitis. The had two recent hospitalizations Chest x-ray admission demonstrated an enlarged, loculated Emergent thoracentesis performed 1500 cc bloody sent cytology. patient’s status improved. ThinPrep block were prepared. Both displayed clusters small round blue cells hyperchromatic nuclei, scant cytoplasm, fine chromatin background rare mesothelial cells, macrophages, numerous lymphocytes. Immunohistochemical (IHC) studies showed CK20, AE1/AE3, CAM 5.2 perinuclear dot-like staining pattern. CD56, chromogranin, synaptophysin also positive. Ki-67 proliferative index about 40%. TTF-1 negative, while CD45 highlighted primary care physician contacted past MCC. Subsequent MCPyV SATB2 nuclear positivity tumor cells. Diagnosis done. Results (if Case Study enter NA) NA Conclusion malignancy rarely fluids. should be included differential diagnosis malignant effusions, especially cases Using IHC, like CK20 markers including newer SATB2, can lead accurate diagnosis. Additional reporting such may increase awareness, where not readily available, as present instance.