Ethnic differences in the effect of parity on breast cancer incidence in premenopausal women in Singapore

Abstract

Differences in the effect of multiparity on breast cancer risk exist in Caucasian, African-American and Hispanic women. Studies in Asian populations are lacking. This thesis proposes that ethnic differences exist in the effect of multiparity on breast cancer incidence in pre-menopausal women in the three major ethnic groups in Singapore. By linkage between the Singapore National Registry of Births and Deaths and the Singapore Cancer Registry, we identified 228,419 mothers, of whom 523 had breast cancer. Through multivariate Cox analysis, the relationship between ethnicity, parity and premenopausal breast cancer risk was examined, adjusted for age at first and last childbirth. The effect of parity on breast cancer risk was shown to be modified by ethnicity. The risk was highest in uniparous Malay women (hazard ratio 1.91 relative to Chinese) and lowest in Indians (HR 0.38). Increased parity reduced the risk in Malays but not in Chinese and Indian women.