Patterns of relapse and second malignancy after adjuvant external beam radiation therapy for stage I-II seminoma.

428Background: To determine relapse rate, patterns of relapse and risk of second malignancy (SM) from a large single institution experience of adjuvant external beam radiation therapy (RT) for stage I-II seminoma. Methods: 463 patients with clinical stage I (n = 339) and II (n = 124) seminoma underwent adjuvant RT (median 25.5Gy) between 2/1990 and 11/2015. Data was gathered by retrospective chart review. Patients with > 5 years of follow-up (n = 312) were included in analysis of SM risk. Of stage II patients, 72% (89/124) received a boost to gross disease (median 4.5Gy). Field design was para-aortic nodal region only (n = 96), para-aortic and ipsilateral pelvic nodal region (n = 351) or para-aortic and bilateral pelvic nodal region (n = 8). Field design was not available for 8 patients. Patients were followed with clinical exam, serial imaging, and tumor markers. Relapse and SM were confirmed pathologically. Results: At median follow-up of 7.9 years, there were 20 relapses (median 13.2 months; range 2.5-...