Late Mortality Among Survivors of Childhood Cancer in Canada: A Retrospective Cohort Study

Children with cancer face an increased risk of complications and death beyond the 5-year survival mark. National surveillance efforts facilitate the systematic tracking of long-term health outcomes, including treatment-related complications and late mortality, among childhood cancer survivors. We aimed to describe the population of 5-year childhood cancer survivors in Canada, quantify the risk of death among survivors relative to the general population, and identify characteristics associated with late mortality.

This retrospective cohort study used the Canadian Cancer Registry linked to the Canadian Vital Statistics-Death database (excludes Quebec). Survivors were diagnosed with cancer before 15 years old (1992-2012) and still alive five years after diagnosis. We approximated the risk of late mortality relative to the general population using standardized mortality ratios (SMRs) and absolute excess ratios (AERs). Cumulative all-cause and cause-specific mortality and time-to-event models identified characteristics associated with late mortality.

Of the 10,800 5-year survivors, 405 (4%) had a late death by 2017 (median follow-up: 9.1 years). Cancer recurrence or progression caused most late deaths (64%), followed by subsequent primary neoplasms (11%) and other health-related causes (15%). Survivors had a higher risk of all-cause mortality than the general population (SMR = 9.4; 95% CI = 8.5-10.4; AER = 34.8, 95% CI = 30.8-38.8). Risk was highest in the first 5-9 years of follow-up. Cumulative mortality differed significantly by age at diagnosis, sex and cancer type.

Our results underline the importance of long-term surveillance of childhood cancer survivors, as mortality rates remain higher than the general population for at least two decades after diagnosis.