45 An Unusual Case of Regression in Merkel Cell Carcinoma

Abstract

Merkel call carcinoma (MCC) is an uncommon aggressive neuroendocrine skin tumor that is typically seen in elderly patients, and characterized by frequent local relapses and a poor prognosis, with survival rates close to only 50% after three years. Here we report a rare case of spontaneous regression of MCC in an 86-year-old man with a medical history of smoking, heart failure, and hypertension. The patient presented with an 8 mm right cheek/lower lid lesion that was noticed six months earlier and was clinically concerning for a basal cell carcinoma or other malignancy. Shave biopsy demonstrated variously sized and shaped dermal aggregations of neoplastic cells with scant cytoplasm and rounded finely granular nuclei. Mitoses were numerous, and many cells were necrotic. Surrounding the tumor was a brisk lymphocytic reaction. Immunohistochemical stains were positive for CK20, CD56, Cam5.2, synaptophysin, and chromogranin, and negative for PanCK, TTF-1, and CK7, consistent with the diagnosis of Merkel cell carcinoma. Tumor extended to the deep margin of the biopsy, and three months later a wide local excision was performed. The excision specimen was entirely submitted for histologic examination, and showed marked solar elastosis with minimal chronic inflammation and dermal fibrosis. No residual carcinoma was identified. Spontaneous regression in MCC is an extremely unusual phenomenon. Only a few cases (25) have been reported in the literature. While regression has been well documented in melanoma and linked to a poor prognosis, in MCC, regression has been associated with improved patient outcomes. The exact mechanism of regression in MCC is still controversial and not well understood, but is theorized to involve apoptosis and a T-cell mediated immune response. Further studies are needed to better understand the role of Meckel cell polyoma virus, induction of CD8 + lymphocytes, and possibly even diet in the development, progression, and regression of MCC.