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SUMMARY
Merkel cell carcinoma (MCC) is a rare neuroendocrine carcinoma of the skin.
Management of MCC is challenging, with overall 5-year survival rates ranging from 30% to 64%. Disease stage is the best predictor for survival, with 5-year survival rates predicted at 81%, 67%, 52%, and 11% for stages I through IV, respectively.
Due to the rarity of the disease, continued multicenter studies and collaboration are required to make necessary strides.
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DON’T FORGET
The clinical appearance of MCC is rather nonspecific. It typically presents as a shiny (83%), well-circumscribed (75%), erythematous (56%) nodule with or without surface ulceration (20%).
Size (tumor diameter) is the strongest prognostic feature.
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CLINICAL PEARLS
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PATIENT EDUCATION POINTS
Due to the role that ultraviolet (UV) radiation has been shown to play in a subset of MCC, prevention is limited to avoidance of and protection from UV radiation exposure and dermatologic screening, especially in high-risk patients such as those who are immunocompromised.
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Merkel cell carcinoma (MCC) is a rare neuroendocrine carcinoma of the skin. The exact mechanisms of carcinogenesis remain incompletely understood. Although prognosis was traditionally dismal, an improved understanding of molecular biology and advancements in targeted therapy have allowed for improved outcomes. The goal of this chapter is to review the epidemiology, pathology, prognosis, and treatment strategies for this rare malignancy.
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MCC is a relatively rare skin cancer with an estimated annual incidence of 0.79 cases per 100,000 persons.1 However, likely because of improved diagnostic tools and an appreciation of the interplay between immunosuppression and MCC, the incidence has been increasing over the last 30 years.2-4 It is primarily a disease of older adults, with an average age of presentation of 69 years. Ninety percent of patients are over age 50.5 A slightly higher incidence is generally observed in males,5,6 but small cohort studies in Finland and China have reported a local slightly higher incidence in females.7-9 MCC occurs most commonly in sun-exposed areas of the body (50% head and neck, 40% extremities).6 Nevertheless, sun-protected regions may also be affected.10 In younger patients, the trunk is the most common site, and in African Americans, the lower extremity is most common.1,11 There appears to be a correlation with the ultraviolet (UV) light radiation index. This is supported by epidemiologic evidence, with the highest reported rates of MCC observed in Hawaii (United States)11-13 and Australia (Global).14,15
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MCC is currently understood to result from two different pathways, with 60% to 80% of cases due to integration of the Merkel cell polyomavirus (MCPyV or MCV) ...