Metastatic Merkel cell carcinoma in the bone marrow of a patient with plasma cell myeloma and therapy-related myelodysplastic syndrome.

Merkel cell carcinoma is an aggressive neoplasm of the skin that shows frequent lymph node metastases, but has only rarely been reported in the bone marrow. Herein we report a case of a 64-year-old male with a history of plasma cell myeloma and recent skin diagnosis of Merkel cell carcinoma who presented for a routine follow-up bone marrow to assess his myeloma. The biopsy showed persistent plasma cell myeloma, trilineage dysplasia, and clusters of neuroendocrine cells consistent with metastatic Merkel cell carcinoma. Discussion of this case, a review of metastatic Merkel cell carcinoma, and identification of clinical settings in which staging bone marrow biopsy may be warranted are presented.