Merkel cell carcinoma of the eyelid.

The Merkel cell is part of the dendritic cell population of the epidermis, and studies suggest it has a role as a slowly adapting mechanoreceptor involved with mediating the sense of touch. Merkel cells can give rise to malignant neoplasms, one tenth of which occur in the eyelid and periocular area, and manifest as painless erythematous nodules, with overlying telangiectatic blood vessels. Merkel cell carcinoma can mimic other malignant lesions, and the diagnosis can be difficult. One third of the tumors recur, and there is a high rate of metastasis. The estimated 5-year survival rate is 38%. Initial treatment should be aggressive, including surgical resection, with consideration of postoperative radiation. Merkel cell carcinoma responds to chemotherapy, but routinely recurs on cessation of treatment. Two cases are presented to illustrate the typical presentation of Merkel cell carcinoma and the importance of electron microscopy and immunohistochemical studies.