Background: South East Asia consists of three major ethnic groups, i.e. Chinese, Malays and Indians. Previous work from our breast cancer research group showed that Malay ethnicity is an independent predictor of poor survival. In this study we evaluate whether (part of) these ethnic survival disparities may be due to ethnic differences in the association of tumor size and lymph node involvement.

Methods: We included all patients diagnosed with breast cancer at the National University Hospital (Singapore) and University of Malaya Medical Center (Kuala Lumpur) between 1990 and 2007, for whom information on tumor size and axillary lymph node status was available (n = 3805). Ethnic differences in the association between tumor size and lymph node involvement were studied and logistic regression analysis was performed to determine the independent effect of ethnicity on the association of tumor size and lymph node involvement.

Results: 1474 patients were categorized as T1 (>0 to 2 cm), 1777 as T2 (2.1 to 5 cm) and 554 as T3 (>5 cm). Within the small tumor size range (>0 to 2 cm) the Malays were significantly more likely to present with node positive disease as compared to the other ethnic groups (36.9% as compared to 24.5% for Chinese and 25.9% for Indians, p value <0.001). Similarly, for tumors measuring 2.1-5 cm, Malays were more likely than Chinese and Indians to have lymph node involvement (59.5%, 50.2% and 52.1%, respectively p value 0.016). After adjustment for age, Progesterone Receptor (PR) status, grade and treatment received, Malay ethnicity was an independent predictor of lymph node involvement, with adjusted Odds Ratio's of 1.4 (95% CI 1.0 to 2.1) for T1 tumors and 1.4 (95% CI 1.1 to 1.9) for T2 tumors compared to Chinese women.

Conclusion: Malay patients are more likely to present with lymph node metastasis especially for the small and midsized tumors as compared to the Chinese and Indians. This could reflect differences in tumor biology between the three ethnic groups with the Malays possibly having more aggressive disease than the others.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P5-14-10.