Table 1. The Ten Most Common Sites for Merkel Cell Carcinoma (MCC), (SEER 1973–2006)a continued...
Many retrospective studies have evaluated the relationship of a wide variety of biological and histological factors to survival and local-regional control.[5,6,15,33,39,41,42,43,44,45,46,47,48,49,50,51,52][Level of evidence: 3iiiDiii] Many of these reports are confounded by small numbers, potential selection bias, referral bias, short follow-up, no uniform clinical protocol for both staging and treatment, and are underpowered to detect modest differences.
A large, single-institution, retrospective study of 156 MCC patients, with a median follow-up of 51 months (range 2–224 months), evaluated histologic factors potentially associated with prognosis.[Level of evidence: 3iiiB] Although this report is subject to potential selection and referral bias, both univariate and multivariate analyses demonstrated a relationship between improved cause-specific survival and circumscribed growth pattern versus infiltrative pattern, shallow-tumor depth versus deep-tumor depth, and absence of lymphovascular invasion versus presence of lymphovascular invasion. Adoption of these findings into a global prognostic algorithm awaits independent confirmation by adequately powered studies.
A 2009 study investigated whether the presence of newly identified MCPyV in MCC tumor specimens influenced clinical outcome among 114 Finnish patients with MCC. In this small study, patients whose tumors were MCPyV+ appeared to have better survival than patients whose tumors were MCPyV-.[Level of evidence: 3iiiDiii] Standardization of procedures to identify and quantify MCPyV and relevant antibodies is needed to improve understanding of both prognostic and epidemiologic questions.
The bulk of MCC literature is from small case series, which are subject to many confounding factors (refer to the Prognostic Factors section of this summary). For this reason, the relapse and survival rates reported by stage vary widely in the literature. In general, lower-stage disease is associated with better overall survival.
Outcomes from patients presenting with small volume local disease and pathologically confirmed cancer-negative lymph nodes report a cause-specific 5-year survival exceeding 90% in one report.[39,50][Level of evidence: 3iiiDiii]
A tabular summary of treatment results of MCC from 12 series illustrates the difficulty in comparing outcome data among series.