The Incidence Of Other Malignancies Before And After Sarcoma Diagnosis: A Population-Based Study.

11076 Background: Sarcomas encompass a group of rare and heterogeneous mesenchymal malignancies with mostly unknown origin. Both exogenous risk factors, in particular radiotherapy, as well as genetic risk factors have been described. Second tumors next to sarcomas suggest associated risk factors. In the current study, we investigate the incidence of sarcomas and other malignancies by using population-based data from the Netherlands Cancer Registry. Methods: In 29,638 patients diagnosed with sarcoma between 1989 and 2015, with a median age of 59 years, we quantified the risk of other malignancies after sarcoma diagnosis using standardized incidence ratios (SIRs). In assessing associations with malignancies before sarcoma diagnosis, we focussed on previous radiotherapy. Skin carcinomas, with the exception of melanomas, were excluded. Results: In total, 3,381 (11.4%) sarcoma patients, median age 71years, had a previous malignancy (at a median age of 66 years). The most frequent sarcomas associated with prior tumors were angiosarcoma (34.5%) and gastrointestinal stromal tumours (20.6%). In the angiosarcoma group, 78.6% of patients had received prior radiotherapy for their previous tumors. Subsequent tumors (diagnosed in patients with median age of 69.5 years) after sarcoma diagnoses were detected in 2,523 patients with median age of 63 years (SIR 1.13; 95%CI: 1.09–1.18). Risks appear notably elevated for breast cancer (SIR 1.19; 95%CI: 1.06–1.34), lung cancer (SIR 1.15; 95%CI: 1.04–1.27), cancers of the urinary tract system (SIR 1.33; 95%CI: 1.14–1.53) and hematological cancers (SIR 1.31; 95%CI: 1.13–1.51). Median time until diagnosis of subsequent cancer was 52.7 months. Conclusions: Sarcoma patients have a markedly increased risk on another malignancy, either before or after the sarcoma diagnosis. Further research into genetic and exogenous risk factors may help to explain the associations.