Declining mortality from breast cancer in Yorkshire, 1983-1998: extent and causes.

Incidence and mortality data, stage of disease and treatment information for female breast cancer were obtained for the years 1975-1999 for the former Yorkshire Regional Health Authority area, from the Northern and Yorkshire Cancer Registry and Information Service. Deaths by age group and 3-year calendar period were separated into those occurring among cases diagnosed 0-2 and 3-4 years preceding death (short- and medium-term survivors, respectively), and among longer-term survivors and age-adjusted rates were calculated separately by survival time. The 3-year survival of cases incident in 1991-1999 and in 1982-1990 were compared, adjusting for stage and treatment. Breast cancer mortality in Yorkshire stopped increasing around 1983 and has since consistently declined, primarily among short- and medium-term survivors. The 3-year survival was significantly improved in cases diagnosed in 1991-1999, compared with 1982-1990, in all age groups (hazard ratio (HR)=0.75, 95% c.l. 0.71-0.78). The improvement was least in the 65+ years age group (HR=0.83, 95% c.l. 0.79-0.88), intermediate in the youngest (<50 years) cases (HR=0.71, 95% c.l. 0.63-0.80) and greatest in the age group 50-64 years, offered routine screening after 1988 (HR=0.51, 95% c.l. 0.47-0.57). The benefit for cases diagnosed in the 1990s persisted, but was reduced after adjustment for stage in cases <65 years, while it disappeared in older cases (HR=1.01). Below age 65 years, the use of systemic therapy increased substantially, but did not explain the residual improvements in short-term prognosis. A greater decline in breast cancer mortality in Yorkshire from 1982 to 1984 was observed among short- and medium-term, than in longer-term, survivors. Much of the improvement in survival in cases <65 years could be attributed to a more favourable stage at diagnosis, whereas this accounted for nearly all the improvement in survival among older cases. Systemic therapy had little or no impact on 3-year survival. Continuing declines in mortality can be expected in the current decade, as a result of the long-term effects of both mammography screening and increased use of systemic therapy.