Background: Merkel cell carcinoma (MCC) is an aggressive skin cancer with a mortality of 33%. Advanced disease at diagnosis is a poor prognostic factor, suggesting that earlier detection may improve outcome. No systematic analysis has been published to define the clinical features that are characteristic of MCC.

Objective: We sought to define the clinical characteristics present at diagnosis to identify features that may aid clinicians in recognizing MCC.

Methods: We conducted a cohort study of 195 patients given the diagnosis of MCC between 1980 and 2007. Data were collected prospectively in the majority of cases, and medical records were reviewed.

Results: An important finding was that 88% of MCCs were asymptomatic (nontender) despite rapid growth in the prior 3 months (63% of lesions) and being red or pink (56%). A majority of MCC lesions (56%) were presumed at biopsy to be benign, with a cyst/acneiform lesion being the single most common diagnosis (32%) given. The median delay from lesion appearance to biopsy was 3 months (range 1-54 months), and median tumor diameter was 1.8 cm. Similar to earlier studies, 81% of primary MCCs occurred on ultraviolet-exposed sites, and our cohort was elderly (90% >50 years), predominantly white (98%), and often profoundly immune suppressed (7.8%). An additional novel finding was that chronic lymphocytic leukemia was more than 30-fold overrepresented among patients with MCC.

Limitations: The study was limited to patients seen at a tertiary care center. Complete clinical data could not be obtained on all patients. This study could not assess the specificity of the clinical characteristics of MCC.

Conclusions: To our knowledge, this study is the first to define clinical features that may serve as clues in the diagnosis of MCC. The most significant features can be summarized in an acronym: AEIOU (asymptomatic/lack of tenderness, expanding rapidly, immune suppression, older than 50 years, and ultraviolet-exposed site on a person with fair skin). In our series, 89% of primary MCCs had 3 or more of these findings. Although MCC is uncommon, when present in combination, these features may indicate a concerning process that would warrant biopsy. In particular, a lesion that is red and expanding rapidly yet asymptomatic should be of concern.