Pathologic nodal evaluation improves prognostic accuracy in Merkel cell carcinoma: Analysis of 5823 cases as the basis of the first consensus staging system

Abstract

Background The management of Merkel cell carcinoma (MCC) has been complicated by a lack of detailed prognostic data and by the presence of conflicting staging systems. Objective To determine the prognostic significance of tumor size, clinical vs pathologic nodal evaluation, and extent of disease at presentation and thereby derive the first consensus staging/prognostic system for MCC. Methods 5,823 prospectively enrolled MCC cases from the National Cancer Data Base (NCDB) had follow-up data (median 64 months) and were used for prognostic analyses. Results At 5 years, overall survival was 40% and relative survival (compared to age- and sex-matched population data) was 54%. Among all MCC cases, 66% presented with local, 27% with nodal and 7% with distant metastatic disease. For cases presenting with local disease only, smaller tumor size was associated with better survival (stage I: ≤2cm: 66% relative survival at five years; stage II: >2cm: 51%; p<0.0001). Patients with clinically local-only disease and pathologically proven negative nodes had better outcome (76% at five years) than those who only underwent clinical nodal evaluation (59%, p<0.0001). Limitations The NCDB does not capture disease-specific survival. Overall survival for MCC patients was therefore used to calculate relative survival based on matched population data. Conclusion Although the majority (68%) of MCC patients in this nationwide cohort did not undergo pathologic nodal evaluation, this procedure may be indicated in many cases as it improves prognostic accuracy and has important treatment implications for those found to have microscopic nodal involvement.