Accurate estimates of cancer survival are important for assessing optimal patient care and prognosis. Evaluation of these estimates via relative survival (a ratio of observed and expected survival rates) requires a population life table that is matched to the cancer population by age, sex, race and/or ethnicity, socioeconomic status, and ideally risk factors for the cancer under examination. Because life tables for all subgroups in a study may be unavailable, we investigated whether cause-specific survival could be used as an alternative for relative survival.
We used data from the Surveillance, Epidemiology, and End Results Program for 2330905 cancer patients from January 1, 1992, through December 31, 2004. We defined cancer-specific deaths according to the following variables: cause of death, only one tumor or the first of multiple tumors, site of the original cancer diagnosis, and comorbidities. Estimates of relative survival and cause-specific survival that were derived by use of an actuarial method were compared.
Among breast cancer patients who were white, black, or of Asian or Pacific Islander descent and who were older than 65 years, estimates of 5-year relative survival (107.5%, 106.6%, and 103.0%, respectively) were higher than estimates of 5-year cause-specific survival (98.6%, 95% confidence interval [CI] = 98.4% to 98.8%; 97.4%, 95% CI = 96.2% to 98.2%; and 99.2%, 95% CI = 98.4%, 99.6%, respectively). Relative survival methods likely underestimated rates for cancers of the oral cavity and pharynx (eg, for white cancer patients aged ≥65 years, relative survival = 54.2%, 95% CI = 53.1% to 55.3%, and cause-specific survival = 60.1%, 95% CI = 59.1% to 60.9%) and the lung and bronchus (eg, for black cancer patients aged ≥65 years, relative survival = 10.5%, 95% CI = 9.9% to 11.2%, and cause-specific survival = 11.9%, 95% CI = 11.2 % to 12.6%), largely because of mismatches between the population with these diseases and the population used to derive the life table. Socioeconomic differences between groups with low and high status in relative survival estimates appeared to be inflated (eg, corpus and uterus socioeconomic status gradient was 13.3% by relative survival methods and 8.8% by cause-specific survival methods).
Although accuracy of the cause of death on a death certificate can be problematic for cause-specific survival estimates, cause-specific survival methods may be an alternative to relative survival methods when suitable life tables are not available.