Abstract
BackgroundCause-specific and relative survival estimates differ. We aimed to examine these differences in common cancers where by possible identifying the most plausible sources of error in each estimate.MethodsTen-year cause-specific and relative survival were estimated for lung, breast, prostate, ovary, oesophagus and colorectal cancers. The cause-specific survival was corrected for misclassification of cause of death. The Pohar-Perme relative survival estimator was modified by (1) correcting for differences in deaths from ischaemic heart disease (IHD) between cancers and general population; or (2) correcting the population hazard for smoking (lung cancer only).ResultsFor all cancers except breast and prostate, relative survival was lower than cause-specific. Correction for published error rates in cause of death gave implausible results. Correction for rates of IHD death gave slightly different relative survival estimates for lung, oesophagus and colorectal cancers. For lung cancer, when the population hazard was inflated for smoking, survival estimates were increased.ConclusionResults agreed with the consensus that relative survival is usually preferable. However, for some cancers, relative survival might be inaccurate (e.g. lung and prostate). Likely solutions include enhancing life tables to include other demographic variables than age and sex, and to stratify relative survival calculation by cause of death.
Highlights
The relative survival is usually lower than the cause-specific, with large differences observed for lung cancer, ovarian cancer and colorectal cancer
In the case of breast, this is because breast cancer patients will have slightly higher socioeconomic status on average than the general population
This can be observed in our data, as when the lifetables are stratified by deprivation, the 10-year survival was the same as the cause-specific survival
Summary
METHODS: Ten-year cause-specific and relative survival were estimated for lung, breast, prostate, ovary, oesophagus and colorectal cancers. The Pohar-Perme relative survival estimator was modified by (1) correcting for differences in deaths from ischaemic heart disease (IHD) between cancers and general population; or (2) correcting the population hazard for smoking (lung cancer only). RESULTS: For all cancers except breast and prostate, relative survival was lower than cause-specific. Correction for rates of IHD death gave slightly different relative survival estimates for lung, oesophagus and colorectal cancers. Relative survival was calculated as a ratio of observed to expected survival in the past.[2] It is more common to calculate it based on subtraction of the expected population hazard rate for death from all causes from the observed hazard of all-cause death in the cancer cohort.[3] Such methods are still generally referred to as relative survival, and we shall do so in this paper. We note here that it is a convenient shorthand rather than an accurate description of the calculation method
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