Merkel cell carcinoma within follicular cysts: report of two cases

Merkel cell carcinoma is a rare cutaneous neoplasm of unknown histogenesis. Several reports have described the association of Merkel cell carcinoma of the skin with other cutaneous neoplasms within the same lesion, and there are also reports describing three examples of Merkel cell carcinoma within follicular cysts. We describe two examples of Merkel cell carcinoma developed within epithelial cysts. Neoplastic cells of Merkel cell tumor expressed immunoreactivity for chromogranin, synaptophysin, neuron-specific enolase, CAM 5.2 and cytokeratin 20, the last two markers showing the characteristic paranuclear dot-like pattern. In contrast, the epithelial wall lining the cyst and surrounding Merkel cell tumor only expressed immunoreactivity for cytokeratin MNF116. The description of five cases of Merkel cell carcinoma within follicular cysts, including the two cases of this report, support some relationship between Merkel cell tumor and the hair follicle.