A Comparison of Late Mortality Among Survivors of Childhood Cancer in the United States and United Kingdom

Background: It is unclear whether late-effect risks among childhood cancer survivors vary internationally. We compared late mortality in the North American Childhood Cancer Survivor Study (CCSS) and British Childhood Cancer Survivor Study (BCCSS). Methods: Late mortality was assessed among 49 822 5-year survivors of childhood cancer diagnosed before 15 years of age from 1970 to 1999 (CCSS, n = 31 596; BCCSS, n = 18 226) using cumulative mortality probabilities (CM%) and adjusted ratios of the standardized mortality ratio. Results: The all-cause CM% at 10 years from diagnosis was statistically significantly lower in the CCSS (4.7%, 95% confidence interval [CI] = 4.5% to 5.0%) compared with the BCCSS (6.9%, 95% CI = 6.5% to 7.2%), attributable to a lower probability of death from recurrence or progression of the primary cancer, with statistically significant differences observed in survivors of leukemia, lymphoma, central nervous system tumors, and sarcoma. However, at 40 years from diagnosis, the CCSS had a greater CM% (22.3% vs 19.3%), attributable to a twofold higher risk of mortality from subsequent malignant neoplasms, cardiac and respiratory diseases, and other health-related causes. Differences increased when assessed by follow-up interval, with the CCSS faring worse as time-since-diagnosis increased. Finally, the gap in all-cause mortality widened more recently, with CCSS survivors diagnosed in 1990-1999 experiencing one-half the excess deaths observed in the BCCSS (ratios of the standardized mortality ratio = 0.5, 95% CI = 0.5 to 0.6). Conclusions: Our findings suggest that US survivors may have received more intensive regimens to achieve sustainable remission and cure, but the cost of this approach was a higher risk of death from late effects. Although the clinical impact of these differences is unclear, our results provide important evidence to aid the discussion of late effects management.