Track: Case Reports

Topic: Neoplasia,Carcinogensis,Tumor Biology

Abstract:

Merkel cell carcinoma (MCC) is a rare and aggressive skin cancer most commonly seen in elderly, Caucasian populations with a history of UV radiation exposure or immunocompromise. Cases have been reported of MCC with overlying squamous cell carcinoma (SCC) or SCC in situ, but there has been less documentation of very large MCC coexisting with large moderately-differentiated SCC as separate lesions on the head. We report a case of a 78-year-old Caucasian man who presented with a 15-centimeter left scalp lesion and a 6-centimeter fungating left cheek mass. Histopathological evaluation for the scalp mass was consistent with moderately-differentiated SCC, and the cheek lesion was consistent with MCC. Due to the extent of the disease, surgery was unreasonable. The patient began immunotherapy with pembrolizumab (Keytruda), a PD-1 inhibitor, to which the MCC responded clinically but the SCC continued to grow. On immunohistochemistry, the MCC was diffusely positive for Preferentially Expressed Antigen in Melanoma (PRAME) with strong intensity in >95% of cells. PRAME is a well-characterized leucine-rich repeat (LRR) cancer-testis antigen within the PRAME family. It is thought PRAME plays a role in the malignant phenotype of some cancer cells, including melanoma and other non-cutaneous malignancies. In contrast to the MCC, PRAME expression in the patient’s SCC was minimal with < 25% of cells and only light intensity. This case illustrates an extraordinary co-occurrence of PRAME-positive MCC with PRAME-negative moderately-differentiated SCC and suggests that PRAME expression may be a predictor of the divergent response of the tumors to initial treatment with pembrolizumab.

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Rachad Mhawej, MD