Childbirth differentially impacts subtype-specific breast cancer risk
MedWire News: A woman's reproductive history differentially affects her risk for triple-negative and estrogen receptor-positive (ER+) breast cancer postmenopause, US study data show.
Women with no children have a lower risk for triple-negative breast cancer but a higher risk for ER+ disease compared with those with at least one child, whereas women with three or more children have a higher triple-negative but lower ER+ breast cancer risk than those with only one child, the researchers report.
Because triple-negative breast cancers are hormone receptor- (ER, progesterone receptor, and human epidermal growth factor receptor 2) negative, it is plausible that established hormonal risk factors for breast cancer could be differentially associated with risk for ER+ versus triple-negative tumor subtypes, explain Amanda Phipps (Fred Hutchinson Cancer Research Center, Seattle, Washington) and colleagues.
Using data from 307 women with triple-negative breast cancer, 2610 women with ER+ breast cancer, and 150,529 without breast cancer enrolled in the Women's Health Initiative, Phipps and team assessed the relationships between reproductive and menstrual history, breastfeeding, oral contraceptive use, and subtype-specific breast cancer risk.
They found that postmenopausal women with no children had a 39% lower risk for triple-negative breast cancer but a 35% higher risk of ER+ disease than women with at least one full-term pregnancy.
On the other hand, among women who had given birth, those with three or more children had a 46% higher risk for triple-negative breast cancer but a 12% lower risk for ER+ disease compared with women with only one child.
The age-adjusted absolute rates of triple-negative breast cancer were 2.71 and 1.54 per 10,000 person-years in parous and nulliparous women, respectively. The respective ER+ breast cancer rates were 21.10 and 28.16 per 10,000 person-years.
Of note, ages at menarche and menopause were only modestly associated with risk for ER+ and not at all with triple-negative breast cancer, while breastfeeding and oral contraceptive use were not associated with either subtype.
However, the lack of association between breastfeeding, oral contraceptive and breast cancer may reflect the older age and postmenopausal status of the study population, compared with other studies, suggest the researchers.
Phipps and co-authors conclude, in the Journal of the National Cancer Institute, that their findings "require further confirmation because the biological mechanisms underlying these differences are uncertain."
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By Laura Dean