Background
Retrospective analysis evaluating the effect of RT dose and treatment volume on locoregional relapse in Merkel cell carcinoma. Patients treated at Moffitt Cancer Center and University of Queensland. Analyzed dose-response relationships and the impact of comprehensive vs. limited nodal RT fields on regional relapse rates.
Interventions and follow up
Arm A: Higher RT dose (≥50 Gy) and/or comprehensive nodal irradiatio
Arm B: Lower RT dose and/or limited field; retrospective comparison within cohort
Primary endpoint: Locoregional relapse
mFollow up: Not specified
Arm B: Lower RT dose and/or limited field; retrospective comparison within cohort
Primary endpoint: Locoregional relapse
mFollow up: Not specified
Results
Dose ≥50 Gy: Associated with improved regional control vs. <50 Gy
Comprehensive nodal RT: Fewer regional relapses than limited-field RT
In-field relapse: Low with adequate dose (<5% at 50 Gy)
Out-of-field relapse: Remaining concern with limited fields; argues for comprehensive nodal irradiation
Comprehensive nodal RT: Fewer regional relapses than limited-field RT
In-field relapse: Low with adequate dose (<5% at 50 Gy)
Out-of-field relapse: Remaining concern with limited fields; argues for comprehensive nodal irradiation
Adverse events
Main adverse events: Dose ≥50 Gy: increased skin and mucosal toxicity at head/neck sites. Comprehensive nodal fields: larger RT volumes with more lymphedema risk vs. limited fields. Grade ≥3 toxicities manageable in this retrospective series.
Conclusions
RT doses ≥50 Gy and comprehensive nodal irradiation achieve better regional control in MCC than lower doses or limited fields. Supports use of 50–56 Gy for definitive/adjuvant RT of MCC. Comprehensive nodal coverage (including clinically uninvolved at-risk basins) reduces out-of-field regional relapse.
Key Limitations
Key Limitations: Retrospective; heterogeneous patient population and treatment approaches; no standardized staging; small sample limits statistical power for dose-response analysis; modern sentinel node biopsy data not consistently used; pre-immunotherapy era.
Clinical Context
Informs current dose recommendations for MCC: adjuvant RT 50–56 Gy to primary site and involved/at-risk regional nodes. For definitive RT (unresectable disease): 60–66 Gy. Lower doses (<50 Gy) are associated with higher regional relapse risk. The concept of elective nodal irradiation for clinically node-negative MCC (based on SNB or imaging) remains debated.
References