This investigation used data from the Waikato breast cancer register to identify all women with newly diagnosed invasive non-metastatic breast cancer diagnosed during 1999–2012, who underwent adjuvant chemotherapy (n=922) or radiation therapy (n=996) as first adjuvant therapy after surgery. The research sought to determine factors associated with delay in adjuvant chemotherapy and radiotherapy for breast cancer, and its impact on the mortality inequity between indigenous Māori and European women in New Zealand. Overall, 32.4% and 32.3% of women experienced delays exceeding the thresholds for chemotherapy (60 days) and radiotherapy (90 days), respectively. Higher proportions of Māori compared with NZ European women experienced delays longer than thresholds for adjuvant radiation therapy (39.8% vs 30.6%; p=0.045) and chemotherapy (37.3% vs 30.5%; p=0.103). In multivariate analysis, factors associated with significantly longer delays for adjuvant therapy included rural compared with urban residency, requiring a surgical re-excision and treatment in public compared with private hospitals (p<0.05). Breast cancer mortality was significantly higher among women who experienced a delay in initiating first adjuvant therapy (HR 1.45; 95% CI, 1.05 to 2.01). Mortality risks were higher among women with delays in chemotherapy (HR1.34; 95% CI, 0.89 to 2.01) or radiation therapy (HR 1.28; 95% CI, 0.68 to 2.40), although these were statistically non-significant
