Second Primary Malignancies in Patients with Colorectal Cancer: A Population-Based Analysis

Abstract

Abstract Purpose This study aimed to profile the characteristics of patients with colorectal cancer (CRC) with a second primary malignancy (SPM) and to identify patients with CRC at high risk of developing SPMs. Methods We retrospectively reviewed data on patients with CRC aged 20–79 years from the Surveillance, Epidemiology, and End Results (SEER) database. Eligible patients were categorized into only one primary malignancy and SPM cohorts. A competing-risk model was used to quantify associations between SPM occurrence and the multiple traits of patients. Finally, a decision curve analysis (DCA) was used to evaluate the clinical usefulness of the model by calculating net benefit. Results A total of 179,884 patients were identified, 18,285 (10.2%) of whom developed SPMs during a maximum follow-up of approximately 18 years. The median survival time after the second diagnosis was less than 4 years. The 3-year, 5-year, and 10-year cumulative risks of developing an SPM were 3.9%, 5.9%, and 10.0%, respectively. According to the multivariable competing-risk model, male colon cancer survivors, older in age, with a well-differentiated tumor and localized disease, who were treated with surgery were susceptible to SPMs. The DCA yielded a wide range of risk thresholds at which the net benefits would be obtained from our proposed model. Conclusion CRC survivors remain at high risk of developing SPMs. Patients with a second diagnosis of cancer showed not only significantly worse survival but also higher cancer-specific mortality. A web-based individualized predictive tool was also provided to assist clinicians in identifying patients at high risk of developing SPMs and planning their future care management.