The Role of Adjuvant Primary Site Radiotherapy for Cutaneous Melanoma Patients with Microsatellitosis.

PURPOSE: The presence of microsatellites in cutaneous melanoma has historically been associated with a poor prognosis. Whether adjuvant primary site radiation therapy (RT) mitigates risk of recurrence is unknown.

METHODS

All patients with cutaneous melanoma who underwent primary site wide local excision at our center between 2016 and 2023 with histopathologic evidence of microsatellites and no clinically involved lymph nodes, in-transit disease, or macrosatellites were retrospectively reviewed. We investigated the association of patient, disease, and treatment factors with recurrence and survival outcomes.

RESULTS

We identified 153 eligible patients with microsatellites. With a median follow-up of 31 months from resection, 3-year local recurrence-free survival (LRFS) was 78% and 3-year disease-free survival (DFS) was 42%. The majority received adjuvant systemic therapy (55%, n = 85 immune checkpoint inhibition; 5%, n = 7 BRAF/MEK-directed therapy). Fifty-nine patients (39%) received postoperative RT after wide local excision. On multivariate analyses with inverse propensity score weighting, receipt of adjuvant primary site RT was associated with longer local recurrence-free survival (LRFS, hazard ratio 0.22, p = 0.04), which appears to drive longer disease-free survival (DFS, hazard ratio 0.46, p = 0.007).

CONCLUSIONS

In the contemporary therapeutic era, even with the majority of patients receiving adjuvant immune checkpoint inhibition or targeted therapy, adjuvant RT is associated with higher local control and DFS. Patients with microsatellitosis should be referred for consideration of postoperative RT.