Treatment and survival disparities by ethnicity in New Zealand women with stage I-III breast cancer tumour subtypes

This study aims to look at the distribution of different subtypes of stage I-III breast cancer in MAori and Pacific versus non-MAori/Pacific women, and to examine cancer outcomes by ethnicity within these different subtypes. This study included 9,015 women diagnosed with stage I-III breast cancer between June 2000 and May 2013, recorded in the combined Waikato and Auckland Breast Cancer Registers, who had complete data on ER, PR and HER2 status. Five ER/PR/HER2 subtypes were defined. Kaplan-Meier method and Cox proportional hazards model were used to examine ethnic disparities in breast cancer-specific survival. Of the 9,015 women, 891 were MAori, 548 were Pacific and 7,576 others. Both MAori and Pacific women were less likely to have triple negative breast cancer compared to others (8.6, 8.9 vs. 13.0%). Pacific women were more than twice as likely to have ER-, PR- and HER2+ cancer than MAori and others (14.2 vs. 6.0%, 6.7%). After adjustment for age, year of diagnosis, stage, grade and treatment, the hazard ratios of breast cancer-specific mortality for MAori and Pacific women with ER+, PR+ and HER2- were 1.52 (95% CI 1.06-2.18) and 1.55 (95% CI 1.04-2.31) compared to others, respectively. MAori women with HER2+ cancer were twice more likely to die of their cancer than others. Outcomes for MAori and Pacific women could be improved by better treatment regimens especially for those with HER2+ breast cancer and for women with ER+, PR+ and HER2- breast cancer.