Incidence of bone and soft tissue sarcoma after radiotherapy: a cohort study of 295,712 Finnish cancer patients.

Radiotherapy is commonly used for treatment of malignant disease. As a consequence of radiotherapy, an increased risk of developing a second malignant neoplasm has been shown. However, little is known about the effects of radiation on developing sarcoma. The aim of this study was to examine the risk of developing a bone or soft tissue sarcoma after radiotherapy for a first primary cancer. The study population included all the patients with primary cancers of breast, cervix uteri, corpus uteri, lung, ovary, prostate, rectum and lymphoma diagnosed during 1953-2000 and identified from the Finnish Cancer Registry. Patients were followed up for subsequent sarcomas. The follow-up yielded 1.5 million person-years at risk and 147 sarcomas. Compared to the national incidence rates, after 10 years of follow-up sarcoma risk was increased among patients who had received neither radiotherapy nor chemotherapy (standardised incidence ratio (SIR) 2.0, 95% CI 1.3-3.0), radiotherapy without chemotherapy (SIR 3.2, 95% CI 2.3-4.3), chemotherapy without radiotherapy (SIR 4.9, 95% CI 1.0-14.4), as well as combined radiotherapy and chemotherapy (SIR 3.4, 95% CI 0.4-12.5). For radiotherapy in ages below 55 the SIR was 4.2 (95% CI 2.9-5.8). In the adjusted regression analysis the rate ratio was 1.5 (95% CI 0.9-2.6) for the radiotherapy group. In conclusion, radiotherapy appears to be associated with an increased risk of developing sarcoma especially among younger patients. Further investigation is needed to clarify the dose-response of the preceding ionizing radiation.