Background
Retrospective analysis of 6,908 MCC cases from the National Cancer Data Base (NCDB) evaluating the impact of adjuvant RT and chemotherapy on overall survival. Largest MCC cohort ever reported. Stages I–III MCC with surgical treatment, stratified by adjuvant therapy. Multivariable analyses adjusted for age, sex, comorbidities, margins, tumor size/site, and lymph node status.
Interventions and follow up
Arm A: Surgery + adjuvant RT
Arm B: Surgery alone (comparator); also evaluated adjuvant chemotherapy ± RT
Primary endpoint: Overall survival
mFollow up: NCDB registry data (2001–2011)
Arm B: Surgery alone (comparator); also evaluated adjuvant chemotherapy ± RT
Primary endpoint: Overall survival
mFollow up: NCDB registry data (2001–2011)
Results
Stage I OS (adjuvant RT): HR 0.71, 95% CI 0.64–0.80, P<.001 — significantly improved
Stage II OS (adjuvant RT): HR 0.77, 95% CI 0.66–0.89, P<.001 — significantly improved
Stage III OS: Neither adjuvant RT nor chemo associated with improved OS
Adjuvant chemotherapy: No OS benefit in any stage
Stage II OS (adjuvant RT): HR 0.77, 95% CI 0.66–0.89, P<.001 — significantly improved
Stage III OS: Neither adjuvant RT nor chemo associated with improved OS
Adjuvant chemotherapy: No OS benefit in any stage
Adverse events
Main adverse events: NCDB database study — treatment toxicity not systematically captured. RT toxicity consistent with field/dose used. Chemotherapy toxicity (carboplatin/etoposide) includes myelosuppression, neuropathy, nausea.
Conclusions
Adjuvant RT is associated with significantly improved OS in Stage I and II MCC, but not Stage III. Adjuvant chemotherapy provides no OS benefit in any stage. This is the largest evidence base supporting adjuvant RT for localized MCC, though it is observational and subject to selection bias.
Key Limitations
Key Limitations: Retrospective NCDB analysis with selection bias; patients receiving RT may have been more fit with better prognosis; incomplete data on recurrence patterns, RT dose/volumes, and extent of surgery; limited follow-up duration; pre-avelumab/pembrolizumab era; no data on Merkel cell polyomavirus status which has prognostic value.
Clinical Context
This NCDB analysis provides the strongest population-based evidence for adjuvant RT in Stage I–II MCC. Combined with the Jouary RCT and institutional series, it strongly supports adjuvant RT as standard of care for resected MCC. NCCN guidelines recommend adjuvant RT for all MCC based on this evidence base. The lack of chemotherapy benefit has largely removed chemo from the adjuvant setting outside of trials.