Merkel cell carcinoma (MCC) typically presents as a solitary dome-shaped, deep red to violaceous nodule or indurated plaque and tends to have a shiny surface, often with overlying telangiectasia. The overlying skin is usually intact. Histologically, anastomosing cords and strands of neoplastic cells are seen in the dermis and subcutis, but not in the epidermis. The individual cells are monomorphous with round vesicular nuclei and scanty, ill-defined cytoplasm. Ultrastructurally the tumor cells are characterized by the presence of paranuclear filament whorls and membrane-bound neurosecretory granules approximately 100 ~ 150 nm across. Immu- nohistochemistry is an important tool in the diagnosis of MCC. The tumor cells have epithelial and neural properties because coexpression of cytokeratin filaments and neurofilaments can be observed. Immunohistochemical study results are positive for neuroendocrine markers (chromogranin, synapto- physin, neurospecific enolase and neurofilaments), low molecular weight cytokeratins and membrane epithelial antigen. Especially, perinuclear dot-like staining for cytokeratin 20 is a characteristic finding.
MCC in general has a poor prognosis with a median survival of 33 to 47 months and has a high incidence of locoregional recurrence and systemic spread. Hematogenous and/or distant lymphatic metastases ultimately occur in one-third of patients and most frequently involve liver, bone, brain, lung and skin, although metastasis to nearly every organ has been reported. Poor prognostic factors are: occurrence in patients aged over 55 years, location on the head and neck region, size of more than 2 cm, the presence of immunosuppression, advanced stage of disease, more than 10 mitotic figures per single high-power field, small cell size, angiolymphatic invasion, and immunoreactivity for CD44. Local recurrence is a major risk factor for further spreading and distant metastases, and worsens the prognosis. Attempts to reduce the rate of loco-regional metastases might also be capable of improving the prognosis.
Treatment modalities for MCC are somewhat controversial but stage specific guidelines are helpful in directing optimal treatment. Current therapeutic guidelines suggest that MCC should be treated with locally aggressive methods including complete surgical excision and post-operative radiotherapy, probably including the locoregional lymph nodes. cialis canadian pharmacy
Surgical excision with wide clinical margin (2~3 cm) is the mainstay of treatment for MCC without distant metastasis (e.g. stage I, II disease). However, MCC usually presents on head and neck areas where conservation of vital organs is important, so some clinicians proposed Mohs micrographic surgery with intraoperative evaluation of the peripheral and deep margins as the preferred surgical approach in locations where sparing healthy tissue is important. Some studies also suggested that local recurrence rate with Mohs micrographic surgery was lower than with wide excision because of thorough histologic evaluation of the margin. But, the true benefit of Mohs micrographic surgery remains unclear.