Exocrine pancreatic cancer as a second primary malignancy: A population-based study.

Backgrounds/Aims: Although cancer survivors are at higher risk of developing second primary malignancies, cancer surveillance strategies for them have not yet been established. This study aimed to identify first primary cancers that had high risks of developing second primary exocrine pancreatic cancer (EPC). Methods: Data on individuals diagnosed with primary cancers between 1993 and 2017 were obtained from the Korea Central Cancer Registry. The standardized incidence ratios (SIRs) of second primary EPCs were analyzed according to the primary tumor sites and follow-up periods. Results: Among the 3,205,840 eligible individuals, 4,836 (0.15%) had second primary EPCs, which accounted for 5.8% of the total EPC patients in Korea. Between 1 and 5 years after the diagnosis of first primary cancers, SIRs of second primary EPCs were increased in patients whose first primary cancers were in the bile duct (males 2.99; females 5.03) in both sexes, and in the small intestine (3.43), gallbladder (3.21), and breast (1.26) in females. Among those who survived 5 or more years after the diagnosis of first primary cancers, SIRs of second primary EPCs were elevated in patients whose first primary cancers were in the bile duct (males 2.61; females 2.33), gallbladder (males 2.29; females 2.22), and kidney (males 1.39; females 1.73) in both sexes, and ovary (1.66) and breast (1.38) in females. Conclusions: Survivors of first primary bile duct, gallbladder, kidney, ovary, and female breast cancer should be closely monitored for the occurrence of second primary EPCs, even after 5 years of follow-up.