Merkel Cell Carcinoma
Merkel cell carcinoma (MCC) is a rare neuroendocrine carcinoma of the skin, typically occurring in adults. It has an aggressive course with spread to regional lymph nodes and distant metastasis. The pathogenesis of MCC involves infection with the Merkel cell polyomavirus combined with other factors such as ultraviolet light exposure and immunosuppression. Clinically, the tumor often presents as a red or violaceous nodule with surface telangiectasia. Histologically, the tumor is composed of monotonous round, blue tumor cells with scant eosinophilic cytoplasm, vesicular nuclei with finely granular chromatin, and multiple nucleoli. There are numerous apoptotic nuclei and frequent mitoses (Fig 13-26). Immunohistochemical studies show that these tumor cells stain with cytokeratin 20 and neuroendocrine markers such as synaptophysin and chromogranin.
The management of MCC is primarily with wide local excision (at least 5-mm margins) and biopsy of regional lymph nodes. Resection requires evaluation of surgical margins with frozen section or Mohs technique. MCC has a high mortality rate compared with other eyelid tumors. The risk of regional and distant metastasis is approximately 30%, and local recurrences are common. Thus, the diagnosis of MCC requires prompt and complete surgical treatment and referral to the appropriate head and neck and oncology specialists.
Figure 13-26 Merkel cell carcinoma (MCC). A, High-magnification photomicrograph shows that the tumor is composed of blue cells with round, granular-appearing nuclei and frequent mitoses. B, Immunohistochemistry with cytokeratin 20 shows the characteristic pattern of perinuclear dotlike staining. Molecular studies for Merkel cell polyomavirus (MCPyV) DNA are positive in approximately 80% of MCCs.
(Courtesy of Tatyana Milman, MD.)
Figure 13-27 Congenital split, or kissing, nevus of the eyelid.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.