Merkel cell carcinoma: clinicopathological aspects of an unusual neoplasm

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. It can occur on the face, the trunk, the genitalia, and the perianal region. The median age of the patients is 69 years, but it may occur earlier and more frequently in immunosuppressed patients. 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 for a definitive diagnosis. The management of MCC is dependent on the 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 followed by radiation therapy. Sentinel lymph node biopsy can be helpful in staging and prognosis, but its benefit in survival remains to be seen. Systemic chemotherapy may be considered as an adjuvant following surgery or to treat locoregional or distant disease. The prognosis of MCC is variable. In patients with localized disease the course is indolent and is 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 outcome most often is seen in patients with early diagnosis and complete excision.