A model of long-term survival following adjuvant therapy for stage 2 breast cancer.

Following adjuvant therapy for breast cancer, some patients will die of this tumour while the remainder will die of other causes. Deaths from breast cancer tend to follow a lognormal distribution, while deaths from other causes can be approximated by national demographic data. By combining these two survival models, we have generated an age-specific method for estimating the impact of treatment on overall long-term survival. Treatment was designed to operate by one of two mechanisms: an increase in cured fraction, or an increase in median tumour-related survival time among uncured patients. This analysis revealed that, for young and middle-aged patients, an increase in cured fraction has substantially greater long-term clinical impact than an increase in median survival time. Unfortunately, the non-parametric tests traditionally used in prospective clinical trials cannot distinguish between these two mechanisms of action.