Trends in the incidence and overall survival of multiple primary cancers in Turkey

Purpose: Multiple primary malignant tumors (MPCs) are defined as at least two histologically distinct malignancies in one individual. We aimed to present the risk of developing multiple primary cancers and to give information about the periods and prediction data regarding survival outcome for MPCs. Methods: All patients with MPCs between 1992-2017 were included in this study. Patients were compared in terms of the primary cancer number, age at diagnosis of first primary cancer, gender, time interval after first cancer detected, cancer types seen mostly together, and the rate of MPCs during the years. Results: The total number of included patients was 117,139. The proportion of patients with MPCs during the follow-up period was 4.95% (n=5,796). Eighteen percent of the cases were synchronous and 82% metachronous. MPCs were most commonly detected in the gastrointestinal tract and were detected more commonly in men than in women (p<0.001). Patients receiving radiotherapy (RT) (p<0.001) and chemotherapy (CT) (p