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

Abstract

428 Background: 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 2.5-55.3 months). There were 9 and 11 relapses in stage I and II patients, respectively, with 7/20 (35%) occurring > 2 years after RT. Relapses were identified by clinical symptoms (n = 7), imaging (n = 9), or elevated serum markers (n = 4). Sites of relapses included the lung/mediastinum (n = 10), retroperitoneum/pelvis (n = 5), bone (n = 3) and inguinal nodes (n = 2). 15 (3 pelvic) occurred after para-aortic and ipsilateral pelvic lymph node RT, while 5 (2 pelvic) occurred after para-aortic RT alone. 19/20 patients received cisplatin-based chemotherapy for relapse and were without evidence of disease at last follow-up (median 123 months). Of 35 total non-testicular SM (33 patients), 17 (48.6%) were in the RT field, 4 (11.4%) were marginal and 14 (40%) were out of field. Common SM were prostate (10), lymphoma (4), bladder (3) and kidney (3). The 5 and 10 year overall survival for the cohort is 99.2% and 97.9%, respectively. Conclusions: Stage I-II seminoma patients have a low risk of relapse and SM following adjuvant RT. Relapse is less common in patients treated with para-aortic and pelvic fields. More than 1/3 of relapses occur more than 2 years after adjuvant RT, necessitating long term clinical, radiographic and biochemical follow-up.