Incidence of second malignancies after external beam radiotherapy for clinical stage I testicular seminoma

Objectives: • To determine the use of adjuvant external beam radiotherapy (EBRT) for patients with clinical stage I testicular seminoma in the USA. • To quantify the risk of specific second primary malignancies (SPMs) associated with radiation exposure in these patients.

Patients and methods: • We used the Surveillance, Epidemiology and End Results database to identify patients diagnosed with clinical stage I testicular seminoma between 1973 and 2000. • We evaluated the use of EBRT in these patients. • We calculated standardized incidence ratios of specific SPMs in these patients. • We stratified the incidence of SPMs based on age at seminoma diagnosis and time to SPM from initial seminoma diagnosis.

Results: • Adjuvant EBRT use declined from the first decade of the study period to the last decade of the study period (80.6% vs 70.2%). • Overall, there was a 19% increase in SPMs in patients exposed to EBRT (observed/expected, O/E, 1.51; 95% CI, 1.08-1.31) compared to the general population. • Specifically, significantly increased risks were observed for thyroid cancer (O/E, 2.32; 95% CI, 1.16-4.16), pancreatic cancer (O/E, 2.38; 95% CI, 1.43-3.72), non-bladder urothelial malignancies (O/E, 4.27; 95% CI, 1.57-9.29), bladder cancer (O/E, 1.47; 95% CI, 1.01-2.28), all haematological malignancies (O/E, 1.44; 95% CI, 1.08-1.89) and non-Hodgkin's lymphoma (O/E, 1.77; 95% CI, 1.22-2.48). • Patients had a persistently elevated risk of SPMs 15 years from the time of initial clinical stage I testicular seminoma diagnosis (O/E, 1.29; 95% CI, 1.10-1.49).

Conclusions: • We confirmed the increased risk of SPMs after EBRT for seminoma, and we identified the specific types of SPMs that develop. • The risk of EBRT-associated SPM persists for years after the initial seminoma diagnosis, and patients should be informed about these long-term risks.