Increased risk of second primary malignancies following uterine cancer: a population-based study in Taiwan over a 30-year period.

BACKGROUND: Previous studies assessing second primary malignancies (SPMs) after uterine cancer have been conducted in Western populations with conflicting results. This study aimed to define the incidence and risk of SPMs in Taiwanese patients with an initial diagnosis of uterine cancer. METHODS: Using population-based data from the Taiwan Cancer Registry for the period 1979-2008, we quantified standardized incidence ratios (SIRs) among 11,571 women with an initial diagnosis of uterine cancer. RESULTS: Among the 11,571 women, 555 (4.80%) developed at least one SPM during 69,987 person-years of follow-up. There was a 71% increased risk of SPM following uterine cancer (SIR=1.71, 95% CI, 1.57-1.86), with higher risks in the vagina/vulva (SIR=9.06), small intestine (SIR=8.45), ovary (SIR=4.15), urinary bladder (SIR=2.31), kidney (SIR=2.24), colorectum (SIR=2.24), lung (SIR=1.96), and breast (SIR=1.43). The risk of SPM was found to be the highest within the first 5 years after diagnosis of uterine cancer, with surveillance bias possibly contributing to the extremely high risk observed in the first follow-up year. The overall risk and pattern of SPM development observed in this study differed from those previously reported in Western populations, possibly because of the methodology and shorter follow-up period employed in this study. The cumulative incidence of SPMs was significantly higher in older patients (≥50 years) than in younger patients (P<0.001). CONCLUSIONS: To our knowledge, this is the first study in an Asian population to report 71% increased risk in SPMs in women previously diagnosed with uterine cancer. A younger age at diagnosis of uterine cancer conferred an increased risk of second malignancies, and SPMs worsened survivorship in patients who survived uterine cancer.