Abstract

Hairy cell leukemia (HCL) and Merkel cell carcinoma (MCC) are rare malignancies arising from distinct cell types. Coexistence of both in a single patient is extremely rare. We present a case of a 63-year-old male who was recently diagnosed with HCL and MCC concurrently.

The patient, who had no previous medical history of malignancy, presented to the Emergency Department with left upper quadrant pain and significant weight loss, as well as a painful rapidly growing skin lesion located on his lower back. Complete blood count and a peripheral smear demonstrated pancytopenia and atypical lymphocytes with cytoplasmic projections, respectively. Imaging revealed splenomegaly with right iliac and inguinal lymphadenopathy. The bone marrow biopsy exhibited diffuse infiltration by leukemic cells, positive for BRAF V600E mutation, diagnostic for HCL. Dermatology was consulted for evaluation of possible cutaneous involvement by HCL. The skin biopsy from the lower back showed malignant basaloid aggregates with neuroendocrine features, and immunohistochemical studies demonstrated positive INSM1, CK20, and chromogranin, supporting the diagnosis of MCC. Complete excision of MCC with subsequent immunochemotherapy for HCL resulted in resolution of both malignancies within 8 months. 

MCC has been linked to hematologic malignancies, most commonly chronic lymphocytic leukemia. A case of simultaneous MCC and HCL diagnosis was reported in 2018. Herein we present an additional case of MCC and HCL, suggesting that the risk of MCC increases with any hematologic immunodeficiency.