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Breast Cancer Res Treat (2009) 113:553558
DOI 10.1007/s10549-008-9947-y
EPIDEMIOLOGY
Helena M. Verkooijen Karen P. L. Yap Vineta Bhalla Khuan Yew Chow Kee Seng Chia
Received: 9 October 2007 / Accepted: 15 February 2008 / Published online: 2 March 2008 Springer Science+Business Media, LLC. 2008
Abstract Background The relationship between multi-parity and premenopausal breast cancer risk is different inCaucasian, African-American and Hispanic women. ForAsian women, this relationship has never been well studied. Methods Within the Singapore Birth Registry, we selected all women who had a rst child between 1986 and 2002 (169,936 Chinese, 40,521 Malay, 17,966 Indian). We linked them to the Singapore Cancer Registry data to identify those who developed breast cancer after childbirth (n = 527). We used multivariate Cox analysis to examine the relationship between parity, ethnicity and premenopausal breast cancer risk. Results Compared to Chinese,Malay women had increased and Indian women had decreased risks of premenopausal breast cancer (adjustedHazard Ratios [HRadj] 1.25 [1.01.6] and 0.48 [0.30.8]
respectively). Multiparity did not modify the risk of premenopausal breast cancer in Chinese and Indians. InMalays there was a signicant risk reduction with increasing parity (Ptrend 0.037). Malay women with one, two and C3 children had premenopausal breast cancer risks (HRadj) of 1.86 (1.23.0), 1.52 (1.12.2) and 0.87 (0.61.3) respectively compared to their Chinese counterparts.Conclusions The impact of multiparity on premenopausal breast cancer risk differs across ethnic groups in Singapore.Increasing parity reduces the risk of premenopausal breast cancer in Malay, but not in Chinese and Indian women.Uniparous Malay women have twice the risk of premenopausal breast cancer compared to uniparous Chinese. This excess risk disappears after giving birth to C3 children.Indian women have lower premenopausal breast cancer risks than Chinese, regardless of their parity status.
Keywords Breast cancer Ethnicity Parity
Population-based Premenopausal
Introduction
Breast cancer is the leading cause of cancer mortality in women world wide [1]. Incidence rates of breast cancer inAsian women are relatively low compared to those ofCaucasian women in industrialized countries. Nevertheless, annual increases in breast cancer incidence and mortality rates in Asian populations are among the highest in the world [2].
Risk factors for breast cancer include low and late parity [3]. Giving birth to multiple children, starting at a young age, reduces a womans risk of breast cancer. The impact...