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 <0.001) had more MPCs than those who never received RT or CT. Survival in MPCs was worse than in single primary cancers. The 5- and 10-year survival rates were 28.1%, and 12.4%, respectively.
Conclusion: We identified approximately 5% MPCs among 117,139 patients in our database. MPCs are more common at 60-69 years in males and at 50-59 years in females. In terms of the risk of MPCs, we should be aware of the cancers that have risk factors, habits, and genetic features commonly affecting primary cancers.