Background: Breast cancer incidence is increasing rapidly among many Asian countries; however, population-based studies with the characterization of tumor subtypes in Asian populations are limited. The objective of this study was to evaluate differences in breast cancer incidence and survival by tumor subtype in an ethnically heterogeneous population in Sarawak, Malaysia.

Methods: The analyses included a total of 1128 invasive breast cancer cases treated at Sarawak General Hospital from 1995 through 2009. As a comparison population, we used NCI's Surveillance, Epidemiology, and End Results (SEER) 9-Registry Databases for breast cancer cases diagnosed during the years 1995 through 1999. Age-frequency density plots were constructed by estrogen receptor (ER) status, ethnicity, and molecular subtype in 1-year age increments. Differences in age at diagnosis between Chinese and non-Chinese participants were determined using Student's t-tests, while differences in categorical tumor characteristics were examined using chi-square test. The Kaplan-Meier method and Cox proportional hazards model were used to assess relapse-free survival.

Results: In the SEER population, ER-positive breast cancers showed a bimodal age distribution with a dominant late-onset, whereas ER-negative tumors had a predominantly early-onset mode. In contrast, the age distribution for the Malaysian women overall showed a predominantly early-onset mode at approximately 45 years, irrespective of ethnicity and/or tumor characteristic. However, compared to non-Chinese women, Chinese women had a slightly older age at diagnosis (median age at diagnosis 52.3 vs. 48.9; p < 0.0001) and a higher proportion of ER-positive tumors (60% vs.51%; p <0.001). Relapse free survival was significantly longer for Chinese than non-Chinese women (p < 0.001). However, after adjusting for age, tumor size, nodal status, grade, and ER status, was not a significant predictor of event free survival (HR = 1.11, 95% CI 0.83 – 1.49). Also, ER expression was an independent predictor of poor relapse free survival (HR = 1.47, 95% CI 1.09 – 1.99). HER 2 positive and triple negative subtypes displayed a significantly worse relapse free survival than Luminal A tumors.

Conclusion: There are distinct ethnic differences in prognosis and tumor subtypes among invasive breast cancer cases in Sarawak, Malaysia. Furthermore, the predominance of early-onset types of breast cancer suggest unique exposure patterns that promote aggressive breast cancer subtypes among all Malaysian women, specifically the non-Chinese group.

Citation Format: Hisani N. Horne, C.R. Beena Devi, Tieng-Swee Tang, Stephen M. Hewitt, William F. Anderson, Xiaohong R. Yang. Differences in breast cancer incidence and survival patterns by tumor subtype and ethnicity in Sarawak, Malaysia. [abstract]. In: Proceedings of the Sixth AACR Conference: The Science of Cancer Health Disparities; Dec 6–9, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2014;23(11 Suppl):Abstract nr C81. doi:10.1158/1538-7755.DISP13-C81

©2014 American Association for Cancer Research.
2014