Analysis of the temporal patterns of benefits in the Health Insurance Plan of Greater New York trial by stage and age.

Reductions in breast cancer mortality in the Health Insurance Plan of Greater New York trial are examined by age at entry and stage at diagnosis using a stage shift cancer screening model. The results indicate that for women aged 40-49 years at entry, benefits are associated with an internal stage shift of stage 1 cancers that have a prognosis poorer than the usual stage 1 cancers. Further, the results indicate that after 18 years of follow-up, of the reduction of 16 fewer deaths in the intervention group, 12-15 of the deaths are related to this internal shift. Given that stage 1 cases inherently have relatively good survival, the time required to see the screening benefit is substantial. For women aged 50-64 years at entry, the results suggest that benefits are associated primarily with shifts to or within stage 1. Further, the results indicate that after 6 years, of the reduction of 31 fewer deaths in the intervention group, 22 of the deaths are related to external shifts to stage 1. Given that stage 2 cancers have poorer survival than stage 1 cancers, screening benefit is seen sooner for the older cohort than for the younger cohort.