Bone marrow involvement with Merkel cell carcinoma.

Merkel cell carcinoma (MCC) is a rare but highly aggressive cutaneous tumour. Most tumours occur in the head and neck, extremities or torso and 36% of them involve the face. Bone marrow involvement in MCC is rare and to our knowledge only nine cases reported in the English literature. Bone marrow biopsy is not usually performed to stage MCC; thus, the true incidence of bone marrow involvement may be under-reported. The majority of the cases reported in the literature have some form of immunosuppression, which suggests a strong association. We report a case of extensive bone marrow involvement from MCC in an 80-year-old Caucasian woman with a history of rheumatoid arthritis treated with adalimumab, methotrexate and prednisone. It may be prudent to include bone marrow biopsy in the staging of MCC in immune-compromised patients. © BMJ Publishing Group Limited 2020. No commercial re-use. See rights and permissions. Published by BMJ.