Background: Several studies have reported an increase in second primary malignancies (SPMs) among gastric cancer patients.
Methods: Patients who were newly diagnosed with gastric cancer between 1997 and 2011 were recruited from the Taiwan National Health Insurance database. Those who had antecedent malignancies or gastrointestinal stromal tumor were excluded. Standardized incidence ratios (SIRs) of SPMs were calculated. Risk factors for cancer development were analyzed by Cox proportional hazards models. Effects of treatments for gastric cancer were treated as time-dependent variables.
Results: During the 15-year study period, 47,729 gastric cancer patients were recruited. Overall, 2,110 SPMs developed during a total follow-up of 137,798 person-years. The SIR for all cancers was 1.46. The SIRs for specific follow-up periods were 1.43, 1.41, and 1.21 at >10 years, 5-10 years, and 1-5 years, respectively. After excluding SPMs that developed within 1 year, significantly higher SIRs were seen for cancers of the head and neck (1.34), esophagus (2.16), colon and rectum (1.37), bones and soft tissues (1.95), ovaries (2.89), bladder (1.47), or kidneys (1.44), as well as non-Hodgkin's lymphoma (5.56). Multivariate analysis showed that age ≥70 years [hazard ratio (HR) 1.19], being male (HR 1.37), diabetes mellitus (HR 1.30), chronic obstructive pulmonary disease (HR 1.17), and liver cirrhosis (HR 1.94) were independent risk factors. Radiotherapy (HR 1.24) and chemotherapy (HR 1.87) were independent risk factors, but surgery (HR 0.67) was not.
Conclusions: Patients with gastric cancer are at increased risk of developing SPM. Close surveillance of patients with risk factors over a longer period should be considered.
Keywords: Gastric cancer; Population-based study; Second primary malignancy.