Life expectancy as a measurement of the benefit shown by clinical trials of treatment for early breast cancer.

Improvements in life expectancy could be a more readily appreciated measure of benefit from a clinical trial than relative risks, odds ratios or increases in survival rate at some arbitrary point in time. Parametric models of survival experience can be used to determine differences in life expectancy. Using the log-normal model, it is shown that the increases in 10-year survival rate found by the overviews of adjuvant systemic therapy trials in early breast cancer are consistent with only small overall increases in life expectancy of about 1 year for Stage I and about 2 years for Stage II. However, if adjuvant therapy transfers a patient from being not cured to being cured, then her life expectancy will have been improved by 16 years for Stage I disease and by 21 years for Stage II. Model analyses on large data sets, such as are available in overviews, could possibly provide some evidence on whether the effect of adjuvant systemic therapy is to increase the cure rate, with the consequent considerable increase in life expectancy for some patients, or whether the effect is only a small increase in life expectancy for those who are not cured.