Merkel cell carcinoma: a review of current advances

Merkel cell carcinoma (MCC) is a rare but aggressive cutaneous malignancy of neuroendocrine origin. Its incidence has tripled over the past 15 years. This article reviews the recent advancement in diagnosis, discoveries in pathogenesis, and updates in management. The acronym, AEIOU, has been proposed to aid in clinical identification. In addition to cytokeratin 20, newer immunohistochemical stains (in particular thyroid transcription factor-1 and neurofilament protein) have proven to be essential in pathologic diagnosis. Although immune suppression and ultraviolet radiation have long been associated with the MCC oncogenesis, recent studies also show involvement of a new polyomavirus and bcl-2. Several tumor classifications have been published in the literature, with the 4-tiered system from Memorial Sloan-Kettering Cancer Center the most widely used. A similar classification with additional distinctions among nodal disease is being constructed. A multidisciplinary treatment algorithm is recommended for MCC. Surgical excision with adjuvant radiotherapy (RT) is indicated for localized tumors. RT is favored over complete lymph node dissection and chemotherapy for regional lymph node involvement. For distant metastasis, management should be individualized with a combination of palliative surgery, RT, and chemotherapy.