MMAP-02 A POPULATION - BASED STUDY ON RADIATION THERAPY FOR BRAIN METASTASIS FROM MALIGNANT MELANOMA IN BRITISH COLUMBIA: EVALUATING THE IMPACT OF IMMUNOTHERAPY AND STEREOTACTIC TECHNIQUES

BACKGROUND: To evaluate population-based outcomes for patients with brain metastasis from malignant melanoma, treated using radiation therapy, and to assess the impact of immunotherapy (IMT) and stereotactic radiation techniques (SRT). METHODS: Data was obtained from the BC Cancer Registry for all patients diagnosed with Melanoma in British Columbia, between 1st Jan 2005 and 31st Dec 2018. A total of 5133 patients were identified. These patients had received 2244 courses of RT, of which 461 were directed to the Brain, in 419 unique individuals. The median age was 62 years and majority, 89.5% (n=375), had cutaneous melanomas while 44 had mucosal or choroidal primary sites of disease. A total of 106 (25.3%) patients received IMT, and pembrolizumab was most commonly used (n=48). Over 85% of patients (n=358) received Whole Brain Radiation Therapy (WBRT) alone, with 20 Gy/5 being the most common dose fractionation. Stereotactic Radio-Surgery (SRS) or SRT alone was used in 31 patients, while 30 patients received a combination of SRS/SRT and WBRT. The most used fractionation for SRS was 30Gy/1 (n=9), and for SRT was 35 Gy/5 (n=25). Overall Survival (OS) was calculated from the date of starting radiation therapy. RESULTS: After a median follow-up of 43 months (95% CI: 18.2 - 67.7), a total of 377 patients had died, with a Median Survival of 2 months (95% CI: 1.46 - 2.53 months) and a 2 year OS of 11.7%. On univariate analysis, age over 65, use of IMT, and SRS/SRT had a significant impact on 2-year OS (14.5% vs 7.4%, p<0.0001; 27.6% vs 6.7%, p<0.0001; and, 38.7% vs. 7.1% p <0.0001, respectively). These factors retained statistical significance on multi-variable analysis. The 2 year OS for patients who received IMT and SRS/SRT alone (n=22) was 54.7%. CONCLUSION: Selected patients treated aggressively with SRS/SRT and IMT have a median survival of >25 months and a 2-year OS > 50%.