Ethnic inequities in use of breast conserving surgery and radiation therapy in Aotearoa/New Zealand: which factors contribute?

PURPOSE: Aotearoa/New Zealand (NZ) faces ethnic inequities with respect to breast cancer survival and treatment. This study establishes if there are ethnic differences in (i) type of surgery and (ii) receipt of radiotherapy (RT) following breast conserving surgery (BCS), among women with early-stage breast cancer in NZ. METHODS: This analysis used Te Rēhita Mata Ūtaetae (Breast Cancer Foundation National Register), a prospectively maintained database of breast cancers from 2000 to 2020. Logistic regression models evaluated ethnic differences in type of surgery (mastectomy or BCS) and receipt of RT with sequential adjustment for potential contributing factors. Subgroup analyses by treatment facility type were undertaken. RESULTS: Of the 16,228 women included, 74% were NZ European (NZE), 10.3% were Māori, 9.4% were Asian and 6.2% were Pacific. Over one-third of women with BCS-eligible tumours received mastectomy. Asian women were more likely to receive mastectomy than NZE (OR 1.62; 95% CI 1.39, 1.90) as were wāhine Māori in the public system (OR 1.21; 95% CI 1.02, 1.44) but not in the private system (OR 0.78; 95% CI 0.51, 1.21). In women undergoing BCS, compared to NZE, Pacific women overall and wāhine Māori in the private system were, respectively, 36 and 38% less likely to receive RT (respective OR 0.64; 95% CI 0.50, 0.83 and 0.62; 95% CI 0.39, 0.98). CONCLUSION: A significant proportion of women with early-stage breast cancer underwent mastectomy and significant ethnic inequities exist. Recently developed NZ Quality Performance Indicators strongly encourage breast conservation and should facilitate more standardized and equitable surgical management of early-stage breast cancer.