Development of Merkel Cell Carcinoma in a Patient Receiving Rituximab.

Merkel cell carcinoma (MCC) is a rare, rapidly growing, and aggressive dermatological neoplasm. It is commonly reported in Caucasian ethnicities, and almost 50% of the patients have a concomitant malignancy and are on immunosuppressive chemotherapy. Here, we present a 79-year-old woman with a history of relapsed Stage II, grade III follicular lymphoma, receiving maintenance rituximab infusions. She presented with a raised erythematous papule on her left cheek. An excisional biopsy of the lesion confirmed a diagnosis of Merkel cell carcinoma. After which, she underwent a wider excision with 1-2 cm margins. PET scan did not reveal any FDG-avid uptake lesions that would be concerning for metastatic disease. However, she underwent a sentinel lymph node biopsy which was also negative. Thus, the diagnosis was finalized as Stage I (T1 N0 M0) MCC. There are only two reported cases in literature about the significant progression of Merkel cell carcinoma in patients who coincidentally were receiving rituximab as a part of treatment for another disease. This raises questions for future investigation and research on whether there is a direct association between rituximab use specifically and the rapid growth of MCC.