Therapeutic radiation for lymphoma and risk of second primary malignant mesothelioma.

PURPOSE: This large, population-based U.S. study of lymphoma patients followed for up to four decades enables detailed analysis of second primary mesothelioma risk after radiotherapy.

METHODS: U.S. Surveillance, Epidemiology, and End Results data were used to identify second primary mesothelioma among patients diagnosed with Hodgkin lymphoma (HL) or non-Hodgkin lymphoma (NHL) between 1973 and 2014. Standardized incidence ratios (SIRs) were calculated by radiotherapy. Multivariate adjusted associations were examined using competing risks survival analysis.

RESULTS: Among 47,219 HL patients (19,538 irradiated) and 252,090 NHL patients (52,454 irradiated), second primary mesothelioma developed among 28 lymphoma patients who received radiotherapy and 59 who did not. Mesothelioma risk was increased among HL and NHL patients treated with radiotherapy [SIR = 1.78, 95% confidence interval (CI) 1.18-2.58], but not without radiotherapy. After multivariate adjustment, radiotherapy was associated with increased mesothelioma risk (relative risk = 1.64, 95% CI 1.05-2.57), especially in lymphoma patients diagnosed before 1995 and after a latency of at least 10 years, and apparently with younger age at diagnosis.

CONCLUSIONS: The increase in second primary mesothelioma risk following radiotherapy for lymphoma is independent of several patient and disease characteristics, and is higher with earlier treatment era and longer latency.