Radiation-Induced Sarcoma: A Retrospective Population-Based Study Over 34 Years in a Single Institution

Aims: About a half of all cancer patients receive radiotherapy as part of their oncological treatment. Because of the carcinogenic effect of ionising radiation, there is a rare, but definite, risk of developing secondary malignancies, including sarcomas. The aim of this retrospective study was to describe the prevalence, patient and tumour characteristics, as well as prognosis and outcome, of patients with radiation-induced sarcomas (RIS) in a cohort of patients treated in the Sarcoma Centre at Aarhus University Hospital over a period of 34 years.

Materials and methods: All patients who fulfilled the criteria for RIS and were treated for RIS in the period 1979-2013 were included. Patient data were retrieved from the Aarhus Sarcoma Registry and the National Danish Sarcoma Database, crosschecked with the National Register of Pathology and validated using the patients' medical records. The primary end point was the effect of surgery and treatment intent on overall survival. Overall survival is reported using the Kaplan-Meier estimates and compared using the Log-rank test. Descriptive statistics are presented for patients, tumours and treatment characteristics.

Results: Of 2845 patients diagnosed with sarcoma between 1979 and 2013, 64 (2%) were diagnosed with RIS. The median interval from the original malignancy was 11 years. The most common histological type was undifferentiated pleomorphic sarcoma (33%). Curative treatment was intended for 45 patients. Fifty patients underwent surgery, of whom 80% had microscopically radical resection (R0). The 5-year overall survival for the whole cohort was 32%. Patients who underwent surgery had a significantly better overall survival compared with patients who were not treated with surgery. In the univariate Cox proportional hazard analyses, no metastases at diagnosis, surgery and R0 resection were favourable prognostics factors of survival.

Conclusion: This study showed that RIS patients are unique in their epidemiology and tumour characteristics. They have a poor prognosis and need special research investigating new intensive treatment strategies to improve the outcome.