Are international differences in breast cancer survival between Australia and the UK present amongst both screen-detected women and non-screen-detected women? survival estimates for women diagnosed in West Midlands and New South Wales 1997-2006

Abstract

We examined survival in screened-detected and non-screen-detected women diagnosed in the West Midlands (UK) and New South Wales (Australia) in order to evaluate whether international differences in survival are related to early diagnosis, or to other factors relating to the healthcare women receive. Data for women aged 50 - 65 years who had been eligible for screening from 50 years were examined. Data for 5,628 women in West Midlands and 6,396 women in New South Wales were linked to screening service records (mean age at diagnosis 53.7 years). We estimated net survival and modelled the excess hazard ratio of breast cancer death by screening status. Survival was lower for women in the West Midlands than in New South Wales (5-year net survival 90.9% [95% CI 89.9%-91.7%] compared with 93.4% [95% CI 92.6%-94.1%], respectively). The difference was greater between the two populations of non-screen-detected women (4.9%) compared to between screen-detected women, (1.8% after adjustment for lead-time and over-diagnosis). The adjusted excess hazard ratio of breast cancer death for West Midlands compared with New South Wales was greater in the non-screen-detected group (EHR 2.00, 95% CI 1.70 - 2.31) but not significantly different to that for women whose cancer had been screen-detected (EHR 1.72, 95% CI 0.87 - 2.56). In this study more than one in three breast cancer deaths in the West Midlands would have been avoided if survival had been the same as in New South Wales. The possibility that women in the UK receive poorer treatment is an important potential explanation which should be examined with care.

Keywords: Australia; New South Wales; UK; West Midlands; breast cancer; cancer screening; excess mortality; mammography; net survival.

Figure 1

(a) Schematic diagram of women eligible for the study alongside (b) a histogram showing the total number of women included in New South Wales (Australia) and the West Midlands (UK) by year of diagnosis (1997–2006).

Figure 2

Schematic diagram demonstrating the exclusion of women in order to adjust for lead‐time bias and over‐diagnosis.

Figure 3

Schematic diagram illustrating (a) net survival estimation correcting for lead‐time bias and over‐diagnosis and (b) the modelling strategy taking into account missing values for extent of disease.

Figure 4

Net survival estimates for women aged 50–65 (mean age 53.7 years) diagnosed with breast cancer 1 January 1997–31 December 2006 and followed up to 31 December 2008. (a) by screening status, New South Wales, (b) by screening status, West Midlands, (c) screen‐detected compared to non‐screen‐detected, New South Wales, (d) screen‐detected compared to non‐screen‐detected, West Midlands.