Merkel cell carcinoma.

Merkel cell carcinoma (MCC) is a rare, aggressive cutaneous cancer that predominately affects elderly Caucasians with fair skin and has a propensity for local recurrence and regional lymph node metastases. A variety of terms have been used to describe this tumor, including trabecular cell carcinoma, neuroendocrine or primary small cell carcinoma of the skin, and anaplastic cancer of the skin. Although the skin lesion is most commonly found on sun-exposed areas of the head and neck or extremities, it can occur on the trunk, genitalia, and perianal region. The median age is 69 years, but it may occur earlier and more frequently in immunosuppressed patients. Patients with MCC frequently present with a nonspecific erythematous or violaceous firm nodule or small plaque that may be surrounded by small satellite tumors. MCC usually arises in the dermis and extends into the subcutis. It may be difficult to accurately diagnose MCC by light microscopy alone and ancillary techniques, including electron microscopy and immunohistochemistry, may be necessary to make a definitive diagnosis. Management of MCC is dependent on stage of the disease and is hampered by its rarity and lack of randomized trials. Nonetheless, for localized disease most guidelines include wide local excision of the primary tumor either alone or with radiation therapy. Sentinel lymph node biopsy can be helpful in staging and prognosis, but its benefit in survival remains to be seen. Systemic chemotherapy, akin to regimens for small cell carcinoma of the lung, may be considered as an adjuvant following surgery or to treat locoregional or distant disease. The prognosis of MCC is variable. Some patients with localized disease have an indolent course and are well controlled with local excision alone. On the other hand, many tumors are aggressive and have a tendency for locoregional recurrence and distant metastases. Such patients have a grim prognosis with a median survival of 9 months. Successful outcomes are most often seen in patients with early diagnosis and complete excision.