Background: We examined second malignancies, a recognized late effect of therapy among survivors of childhood and adolescent cancer, among a recent, population-based cohort of 2,322 5-year survivors diagnosed before 20 years of age in British Columbia (BC), Canada between 1970 and 1995.
Procedure: Survivors and second malignancies were identified from the BC Cancer Registry. Risk of second malignancy was evaluated using standardized incidence ratios (SIRs), absolute excess risk (AER), and cumulative risk. The effect of demographic, temporal, and disease-related characteristics on risk was assessed.
Results: Fifty-five second malignancies were observed after 26,071 person-years of follow-up. Relative rate of developing a second malignancy among survivors was 5 times higher than expected (SIR = 5.0, 95% CI, 3.8-6.5), and absolute excess risk was 1.7 deaths per 1,000 person-years. Cumulative incidence of a second malignancy was 5.1% at 25 years after diagnosis of the first cancer. SIRs and absolute excess risk of subsequent cancer was higher among females (SIR = 5.9, 95% CI, 4.5-8.3 and AER = 2.66). While relative risk of second cancer was higher for those diagnosed before 10 years of age (SIR = 10.6, 95% CI, 7.1-16.0), absolute excess risk was slightly higher for those diagnosed after 10 years of age. SIRs were significantly elevated for all follow-up periods, but absolute excess risk of a second cancer was highest among patients surviving more than 15 years.
Conclusions: Increased risk of a subsequent neoplasm is evident among childhood cancer survivors diagnosed in more recent periods than has been previously reported, continues years after diagnosis, and varies according to several risk factors. Continued surveillance is essential to quantify and characterize long-term and changing risks for appropriate follow-up.