CASE OF THE MONTH
64 year old male who presents with multiple skin tumors on his right temporal area. Histologic sections show an infiltrate of malignant cells situated within the papillary and reticular dermis with no obvious epidermal involvement. The malignant cells are arranged in nests and trabeculae. They demonstrate neuroendocrine features: nuclear molding, “salt and pepper” chromatin, high N/C ratio and indistinct nucleoli. Numerous mitotic figures are seen. The tumor cells are positive for CK8/18, BCL2 (variable), chromogranin (variable) and synaptophysin. CD56 marks rare tumor cells. CK20 marks rare tumor cells with dot-like positivity. The tumor cells are negative for S100 (predominantly) and Melan-A.
Merkel cell carcinoma is an uncommon, highly aggressive primary cutaneous neuroendocrine carcinoma typically affecting eldering and immunocompromised individuals with a male predominance. It typically affects sun exposed areas, such as the head and neck. The differential diagnosis includes metastatic neuroendocrine carcinoma in the skin. Treatment includes wide local excision sentinel lymph node biopsy with or without radiation. Emerging biologic treatments target PDL1/PD1 pathways. Prognosis is very poor with high mortality rate.