Table 1. The Ten Most Common Sites for Merkel Cell Carcinoma (MCC), (SEER 1973–2006)a continued...
The significance of the new MCPyV findings remains uncertain. The prognostic significance of viral load, antibody titer levels, and the role of underlying immunosuppression in hosts (from disease and medications) are under investigation.
Prevalence of MCPyV appears to differ between MCC patients in the the United States and Europe versus Australia. It has been suggested that there may be two independent pathways for the development of MCC: one driven by the presence of MCPyV, and the other driven primarily by sun damage, especially as noted in patient series from Australia.[21,25,31]
Although no unique marker for MCC has been identified, a variety of molecular and cytogenetic markers of MCC have been reported.[5,8,14]
MCC usually presents as a painless, indurated, solitary dermal nodule with a slightly erythematous to deeply violaceous color, and rarely, an ulcer. MCC can infiltrate locally via dermal lymphatics, resulting in multiple satellite lesions. Because of its nonspecific clinical appearance, MCC is rarely suspected prior to biopsy. Photographs of MCC skin lesions illustrate its clinical variability.
A mnemonic  summarizing typical clinical characteristics of MCC has been proposed:
- E=Expanding rapidly.
- I=Immune suppressed.
- O=Older than 50 years.
- U=UV-exposed skin.
Not all patients have every element in this mnemonic; however, in this study, 89% of patients met three or more criteria, 52% met four or more criteria, and 7% met all five criteria.
Initial Clinical Evaluation
Because local-regional spread is common, newly diagnosed MCC patients require a careful clinical examination that includes looking for satellite lesions and regional nodal involvement.
An imaging work-up should be tailored to the clinical presentation as well as any relevant signs and symptoms. There has been no systematic study of the optimal imaging work-up for newly diagnosed patients, and it is not clear if all newly diagnosed patients, especially those with the smallest primaries, benefit from a detailed imaging work-up.
If an imaging work-up is performed, it may include a computed tomography (CT) scan of the chest and abdomen to rule out primary small cell lung cancer as well as distant and regional metastases. Imaging studies designed to evaluate suspicious signs and symptoms may also be recommended. In one series, CT scans had an 80% false-negative rate for regional metastases. Head and neck presentations may require additional imaging. Magnetic resonance imaging has been used to evaluate MCC but has not been studied systematically. Fluorodeoxyglucose-positron emission tomography results have been reported only in selected cases.[35,36] Routine blood work as a baseline has been recommended but has not been studied systematically. There are no known circulating tumor markers specifically for MCC.