A rare involvement in skin cancer: Merkel cell carcinoma with bone marrow infiltration in a kidney transplant recipient.

A 60-year-old man presented with a painless, rapidly growing, haemorrhagic pink nodule on the posterior of his thigh that had developed 1 month previously. He had a diagnosis of IgA nephropathy and had received a renal allograft 7 years before. An excisional biopsy was performed and the diagnosis of Merkel cell carcinoma (MCC) was made. No distant metastases was detected. 10 months after first presentation, due to the development of acute pancytopenia and concomitant FDG PET/CT findings compatible with disease progression, bone marrow biopsy was performed which revealed metastasis of MCC. Dermatologists and oncologists should be aware that MCC could potentially involve the bone marrow in organ transplant recipients. In the follow-up period, a complete blood count should be carried out; FDG PET/CT can be obtained to follow up the metabolic status of the disease and bone marrow biopsy should be performed if necessary.