Previous studies into this area have shown survival from cancer being lower for Pacific compared to Maori women, with both being less than other ethnicities. This paper used audit data to examine differences between the groups on characteristics of their cancers, as well as patient attributes like age and residence. This was then used to adjust survival calculations to see if these factors may explain the original differences in survival.
Breast cancer and patient differences
Compared with other ethnicities, Maori and Pacific women:
- were younger
- came from more disadvantaged areas
- had larger cancers
- had more ductal cancers (cancer that began in the milk ducts) and fewer lobular cancers (cancer began in the milk-producing lobules, which empty out into the ducts)
- were less likely to have triple negative cancers (negative for all three hormonal receptor tests, therefore, will not respond to hormonal therapy)
- had more HER2 positive cancers (HER2 is a protein which promotes growth of cancer cells)
In addition, more Pacific women had vascular invasion (cancer spread to blood). Maori women were more likely to live in areas far from regional cancer centres, whereas Pacific women generally lived closer to these centres.
Survival
This study found that, even after adjusting for the patient and cancer characteristics described above, as well as other common factors that have been shown to affect survival, Maori women still had reduced breast cancer survival compared with other New Zealand women. The survival for Pacific women was also low, but the difference between Pacific and other women was not significant after adjustment.