Estimating breast cancer-specific and other-cause mortality in clinical trial and population-based cancer registry cohorts.

BACKGROUND: To compute net cancer-specific survival rates using population data sources (eg, the National Cancer Institute's Surveillance, Epidemiology, and End Results [SEER] Program), 2 approaches primarily are used: relative survival (observed survival adjusted for life expectancy) and cause-specific survival based on death certificates. The authors of this report evaluated the performance of these estimates relative to a third approach based on detailed clinical follow-up history.

METHODS: By using data from Cancer Cooperative Group clinical trials in breast cancer, the authors estimated 1) relative survival, 2) breast cancer-specific survival (BCSS) determined from death certificates, and 3) BCSS obtained by attributing cause according to clinical events after diagnosis, which, for this analysis was considered the benchmark "true" estimate. Noncancer life expectancy also was compared between trial participants, SEER registry patients, and the general population.

RESULTS: Among trial patients, relative survival overestimated true BCSS in patients with lymph node-negative breast cancer; whereas, in patients with lymph node-positive breast cancer, the 2 estimates were similar. For higher risk patients (younger age, larger tumors), relative survival accurately estimated true BCSS. In lower risk patients, death certificate BCSS was more accurate than relative survival. Noncancer life expectancy was more favorable among trial participants than in the general population and among SEER patients. Tumor size at diagnosis, which is a potential surrogate for screening use, partially accounted for this difference.

CONCLUSIONS: In the clinical trials, relative survival accurately estimated BCSS in patients who had higher risk disease despite more favorable other-cause mortality than the population at large. In patients with lower risk disease, the estimate using death certificate information was more accurate. For SEER data and other data sources where detailed postdiagnosis clinical history was unavailable, death certificate-based estimates of cause-specific survival may be a superior choice.