Age-related differences in colon and rectal cancer survival: An analysis of United States SEER-18 data

Age-related differences in colon and rectal cancer survival have been observed, even after accounting for differences in background mortality. To determine to what extent stage, tumour site, or histology could contribute to these differences, we estimated 1-year relative survival (RS) age stratified by these factors. Colon and rectal cancer cases diagnosed between 2012 and 2016 and followed up until 2017 were retrieved from 18 United States Surveillance Epidemiology and End Results cancer registries. For colon cancer, 1-year RS ranged from 87.8% [95% Confidence Interval: 87.5-88.2] in the 50-64-year-old age group to 62.3% [61.3-63.3] in the 85-99-year-old age group and for rectal cancer ranged from 92.3% [91.8-82.7] to 65.0% [62.3-67.5]. With respect to stage, absolute differences in RS between 50-64-year-old and 75-84-year-old in RS increased with increasing stage (from 6 [5-7] %-points in localized disease to 27 [25-29] %-points in distant disease) and were the highest for cancers of unknown stage (>28%-points). With respect to topography, age-related differences in survival were smallest for those in right-sided colon (8 [7-9] %-points) and largest for tumours of the colon without topography further specified (25 [21-29] %-points). While age-related differences in survival varied by histology and tumour site, the overall age-related differences in survival could not be explained by differences in distribution of these factors by age, consistent with a hypothesis that stage at diagnosis or treatment are more likely drivers. Incorporating data on geriatric conditions such as frailty and comorbidity would support further understanding of the age gap in colon and rectal cancer survival.