172 - The Role of Adjuvant Primary Site Radiotherapy for Patients with Cutaneous Melanoma Microsatellitosis
Presenter(s)
K. N. Nordlund1, A. Devireddy2, R. Lin1, A. F. M. Salem Jr1, N. X. Yang1, S. Keatts1, A. Farooqi3, A. J. Bishop3, B. A. Guadagnolo3, R. Weiser1, S. Fisher1, R. P. Goepfert1, M. I. Ross1, R. Amaria1, J. McQuade1, I. Glitza4, A. K. Yoder3, and D. Mitra3; 1The University of Texas MD Anderson Cancer Center, Houston, TX, 2McGovern medical school, Houston, TX, 3Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 4The University of Texas, MD Anderson Cancer Center, Houston, TX
Purpose/Objective(s): Patients with melanoma microsatellites are at high risk of locoregional recurrence and poor overall outcomes. There is an absence of data evaluating adjuvant primary site radiotherapy (APS-RT) in the context of available immune checkpoint inhibitors (ICI) and targeted therapies (TT). This study evaluates the effect of APS-RT on outcomes for patients with microsatellites in the modern era.
Materials/Methods: We identified 156 patients with cutaneous melanoma microsatellites who underwent surgical excision at our center between 2016-2023, with no distant metastases, clinically involved nodes, in-transits, or macrosatellite disease. Clinical factors in patients with and without APS-RT were compared by Fisher’s Exact, Mann Whitney, or Chi Square testing. The Kaplan Meier method was used to assess outcomes with Log Rank testing for univariate predictors and Cox Proportional Hazards testing to construct multivariate models.
Results: The overall population was 67% male (n=104) with a median age of 66 (IQR 53-76). The most common anatomic site was head and neck (36%, n=56). Additional risk factors for local recurrence (LR) were: 44% (n=68) ulceration, 39% (n=60) perineural invasion and 8% (n=12) positive margin resection. Median Breslow thickness was 4.0 mm (IQR 2.3-7.0). 139 (89%) had sentinel lymph node biopsy. Microscopic nodal disease was common (60%, n=93).
Sixty percent received adjuvant systemic therapy (88 ICI and 6 TT) and 38% (n=60) received APS-RT. There were no significant differences in patient, disease or treatment factors between patients receiving or not receiving APS-RT. However, APS-RT was more common in recent years (19% pre-2019 vs. 55% since 2019, p<0.001). At a median 31 months (IQR 19-50) since resection, 29 patients developed LR with 3-year LR 78%. Better local control (LC) was seen following R0 resection (3-yr LC 82% vs. 36%, p=0.01) and APS-RT (3-yr LC 89% vs. 72%, p=0.013). These factors were also associated with better DFS (R0: 3-yr DFS 46% vs. 0%, p=0.001 and APS-RT 3-yr DFS 58% vs. 34%, p=0.009). Adjuvant ICI or TT were not associated with better LC but were associated with better DFS (3-yr DFS 50% vs. 29%, p=0.038). On multivariate analysis these effects persisted with a lower risk of LR with APS-RT (HR 0.28, 95%CI 0.10-0.73, p=0.01), R0 resection (HR 0.28, 95%CI 0.11-0.68, p=0.005), and non-head and neck anatomic site (HR 0.41, 95%CI 0.19-0.85, p=0.02). Similarly, patients experienced better DFS with APS-RT (HR 0.53, 95%CI 0.33-0.85, p=0.008), R0 resection (HR 0.36, 95%CI 0.19-0.68, p=0.002), adjuvant systemic therapy (HR 0.60, 95%CI 0.39-0.92, p=0.021), and absence of nodal disease (HR 0.60, 95% CI 0.37-0.60, p=0.036).Conclusion: APS-RT improves LC for patients with cutaneous melanoma microsatellitosis in the contemporary therapeutic era. Our data also suggests APS-RT improves DFS in this patient population at high-risk for locoregional relapse.