Genomic analysis reveals somatic mutations of ATM gene in DNA repair confer exceptional target lesion response to radiation therapy.

130 Background: Somatic mutations of genes involved in DNA repair (e.g. ATM and BRCA1/2) may result in chemotherapy resistance and poor prognosis, but may confer sensitivity to radiation therapy. In this study, we aimed to the hypothesis that patients with such mutations may be more susceptible to radiotherapy. Methods: Using prospectively collected RT registry, we identified patients who underwent both RT to gross disease and NGS panel screening between 2013 and 2019 (N = 27,664). From a cohort of 134 patients, 33 patients with somatic mutation in ATM or BRCA 1/2 were identified and closely matched with 33 patients without mutation using propensity score based on radiation dose and histology. Results: Infield response rate was evaluated in 66 patients with 90 gross lesions (ATM mutation, 11 patients and BRCA 1/2 mutation, 22 patients). The median tumor size and RT dose was 24 mm (3-140) and 40 Gy (12-66), respectively. Stark differences were seen in infield complete response rate, overall response rate, and local control rate at target lesions by ATM mutation (mutation vs. no mutation; 50% vs. 8%, 61% vs. 24%, and 94% vs. 58%, P < .05). Response duration was also longer ATM mutation (median 11 vs. 3 months, P = .001). However, RT-related toxicities were not different (17% vs. 11%, P = .515) and no severe toxicity occurred. Conclusions: ATM mutations confer exceptional responses to radiation therapy, even with palliative dose, which has potential therapeutic implications.