Risk factors associated with mortality from breast cancer in Waikato, New Zealand: a case-control study

The aim of this study is to identify key characteristics associated with mortality from breast cancer among women with newly diagnosed breast cancer in New Zealand (NZ).

Case-control study.

All primary breast cancers diagnosed between 01/01/2002 and 31/12/2010 in Waikato, NZ, were identified from the Waikato Breast Cancer Register. A total of 258 breast cancer deaths were identified from 1767 invasive cancers diagnosed over this period.

Breast cancer deaths (n = 246) were compared with an age and year of diagnosis matched control group (n = 652) who were alive at the time of the death of the corresponding case and subsequently did not die from breast cancer. Diagnosis through symptomatic presentation, advanced stage, higher grade, absent hormone receptors (i.e. oestrogen and progesterone) and HER-2 amplification were associated with significantly higher risks of breast cancer mortality in bivariate analysis. Tumour stage, grade and hormone receptor status remained significant in the multivariable model, while mode of detection and HER-2 status were non-significant. In the bivariate analysis, Māori women had a higher risk of breast cancer mortality compared to NZ European women (OR 1.34) which was statistically non-significant. However in the adjusted model, risk of mortality was lower for Māori compared to NZ European women, although this was not significant statistically (OR 0.85).

Mortality pattern from breast cancer in this study were associated with established risk factors. Ethnic inequity in breast cancer mortality in NZ appears to be largely attributable to delay in diagnosis and tumour related factors. Further research in a larger cohort is needed to identify the full impact of these factors on ethnic inequity in breast cancer mortality.