Metastatic Basal Cell Carcinoma with Neuroendocrine Differentiation or Merkel Cell Carcinoma

We present here a case of basal cell carcinoma (BCC) with neuroendocrine features that has transformed into a high-grade neuroendocrine carcinoma with various morphologic features of Merkel cell carcinoma (MCC). A 54-year-old white female was treated for a BCC of the right thigh. Pathologic examination revealed an otherwise classical BCC that demonstrated granular positivity for chromogranin. Six years later the patient developed a right inguinal lymphadenopathy diagnosed as metastatic BCC with squamous changes. The metastatic BCC showed partial peripheral palisading and a trabecular pattern. Two years later the patient underwent a right nephrectomy due to obstruction of the right ureter by metastatic BCC. After another four years the patient came back with extensive involvement of the appendiceal wall and right ovary by a diffusely infiltrating metastatic basaloid and trabecular carcinoma. This time the tumor had many histologic features of MCC and showed strong positivity for chromogranin and also for CK20 and NSE. Electron microscopy revealed neurosecretory granules. This case is an example of a chromogranin positive basal cell carcinoma of the skin, which transformed during multiple recurrences into a high grade neuroendocrine carcinoma with features of Merkel cell tumor, demonstrating the potential for cross differentiation among skin tumors.