Background
Phase III randomized controlled trial evaluating adjuvant prophylactic regional radiotherapy vs. observation in Stage I Merkel cell carcinoma (T1–T2 N0 M0 after complete surgical excision). 83 patients. The first and only randomized trial in MCC. Primary endpoint: locoregional relapse-free survival. All patients had clear surgical margins with ≥1 cm excision margin.
Interventions and follow up
Arm A: Adjuvant RT to primary site and regional nodes (postoperative RT, 50 Gy in 25 fractions)
Arm B: Observation after surgery
Primary endpoint: Locoregional relapse-free survival
mFollow up: Median 36 month
Arm B: Observation after surgery
Primary endpoint: Locoregional relapse-free survival
mFollow up: Median 36 month
Results
Locoregional Relapse (observation): 16.7%
Locoregional Relapse (adjuvant RT): 0%
P-value: P=.007 — statistically significant
OS: No significant difference between arms
Grade ≥3 toxicity (RT): 8%
Locoregional Relapse (adjuvant RT): 0%
P-value: P=.007 — statistically significant
OS: No significant difference between arms
Grade ≥3 toxicity (RT): 8%
Adverse events
Main adverse events: Adjuvant RT: grade ≥3 toxicity 8% (skin reactions, mucositis for H&N sites). Grade 1–2 toxicity common (erythema, fatigue). Acceptable toxicity for preventive intent treatment.
Conclusions
Adjuvant prophylactic RT to the primary site and regional nodes eliminates locoregional relapse in Stage I MCC (0% vs 16.7%, P=.007). This is the only RCT in MCC, providing Level I evidence for adjuvant RT in resected Stage I disease, despite no OS benefit in this small trial.
Key Limitations
Key Limitations: Small sample (n=83); trial stopped early; limited statistical power for OS; heterogeneous RT volumes; 36-month median follow-up relatively short for MCC where late relapses occur; pre-immunotherapy era; SLN biopsy not consistently used for pathologic staging.
Clinical Context
This is the only Level I evidence for adjuvant RT in MCC. Combined with the Bhatia NCDB analysis, it strongly supports adjuvant RT as standard of care after complete resection of MCC. NCCN guidelines recommend adjuvant RT for all MCC (primary site ± regional nodes based on SLN status). The only ongoing discussion is RT field extent — whether elective nodal RT is needed in SNB-negative disease.
References