Ethnic differences in non-metastatic breast cancer outcomes by tumour subtype: Real-world data from the Singapore Joint Breast Cancer Registry.

e13772 Background: Ethnic disparities in breast cancer (BC) are increasingly recognized, with emerging differences among different Asian ethnicities. We examined the relationship between ethnicity and recurrence-free interval (RFI) and overall survival (OS) among female BC patients in the Singapore Joint Breast Cancer Registry (JBCR). Methods: Patient-level data from 4 participating institutions in JBCR on BC diagnosed between January 2000 and December 2017 were used. Fine and Gray regression and Cox proportional hazard regression models were performed to evaluate ethnic differences in RFI and OS respectively, overall and by subtype (hormone receptor-positive HER2 negative [HR+HER2-], hormone receptor-positive HER2-positive [HR+HER2+], hormone receptor-negative HER2-positive [HR-HER2+] and triple negative [TNBC]. Multivariable (MV) models were adjusted for age, marital status, body mass index, comorbidities, receipt of medical subsidies, stage, grade, subtype and treatment factors (surgery, radiotherapy, chemotherapy, endocrine therapy). Results: A total of 14,577 Stage I-III BC cases with a median follow-up of 11.5 years were analysed. Overall stage distribution was I (34.6%), II (43.0%) and III (22.4%). Stage III was more common in Malay (37.0%) and Indian (25.6%) women than Chinese (20.5%) and other ethnicities (22.4%) (p < 0.001). Overall subtype distribution was HR+HER2- (54.1%), HR+HER2+ (14.4%), HR-HER2+ (9.3%) and TNBC (10.8%). TNBC was more common in Indian (15.0%) than Chinese (10.4%), Malay (11.5%) and other ethnicities (10.0%) (p < 0.001). Overall 5-year RFI and OS were 84.3% and 87.5% respectively. Malay and Indian women had significantly lower 5-year RFI (76.6% and 81.1%) compared to Chinese (85.3%) and other ethnicities (85.6%) (p < 0.001). 5-year OS was also lower for Malay and Indian versus Chinese and other ethnicities (81.2% vs 85.0% vs 88.3% vs 88.6%, p < 0.001). In overall MV analysis, compared to Chinese, risk of recurrence (Malay: hazard ratio [HR] 1.25; 95% CI 1.11 – 1.41; Indian: HR 1.20; 95% CI 1.04-1.38) and risk of death (Malay: HR 1.32; 95% CI 1.19 – 1.47; Indian: HR 1.23; 95% CI 1.08-1.40) remained higher in Malay and Indian women. The HR+HER2- subtype showed similar findings, with higher risks of recurrence and death for Malay and Indian women compared to Chinese (RFI - Malay: HR 1.33; 95% CI 1.13 – 1.57; Indian: HR 1.34; 95% CI 1.10-1.64 and OS - Malay: HR 1.45; 95% CI 1.24 – 1.68; Indian: HR 1.34; 95% CI 1.11-1.62). No significant ethnic differences in RFI or OS were observed within each of the other tumour subtypes after adjustment in MV analysis. Conclusions: The disparities in BC outcomes between different Asian ethnicities in Singapore are most pronounced in the HR+HER2- subtype. Further work is needed to unravel ethnicity-related biological factors and other determinants of health for strategies to promote equity.