Multiple primary tumors in patients with surgically treated pancreatic cancer: a SEER population-based study.

Background: With improving survival after pancreatic cancer (PC) resection, questions emerge concerning risk and patterns of metachronous tumors. We aimed to determine the incidence of multiple primary cancers among postoperative PC survivors. Methods: Patients undergoing PC surgery from 1975 to 2020 were identified in the Surveillance, Epidemiology, and End Results (SEER) registry. Standardized incidence ratios (SIRs) compared observed-to-expected cancers based on U.S. population rates. Cumulative incidence of secondary tumors was analyzed with Cox regression and cancer-specific survival with Kaplan-Meier curves. Results: Of 6,100 resected PC patients, 267 (4.38%) developed multiple cancers over 6.2 years median follow-up period. Subsequent malignancies showed a rising cumulative incidence extending beyond 5 years. Lung cancer was the predominant second primary in both males (n=36, SIR 1.87) and females (n=32, SIR 2.17). Prostate (n=33) and breast (n=25) cancers were also common. Risk varied by latency period and gender. Conclusions: Postoperative PC patients face a measurable risk for secondary cancers. Enhanced long-term surveillance has the potential to improve early detection and outcomes in this survivor population. Our data provides real-world evidence which could help inform surveillance guidelines in the future.