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.