Three histologic subtypes of MCC have been described. Although largely supplanted by immunohistochemistry, electron microscopy can be used to confirm the diagnosis of MCC when needed. The most characteristic findings are perinuclear bundles of intermediate filaments and electron-dense neurosecretory granules. Like melanoma, MCC has a high propensity for local recurrence, regional lymph node spread, and distant metastases. Spread of MCC occurs in a predictable fashion.
Initial spread is to first-echelon lymph nodes.
Subsequent spread occurs to higher-order nodal regions, then to distant sites. The presence of regional nodal or distant metastases adversely affects survival. Treatment is dictated by the clinical stage at presentation and may involve surgery, radiotherapy, and chemotherapy. In many respects, treatment for MCC resembles treatment for malignant melanoma. The treatment of choice for the primary lesion in MCC is surgical excision.