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. 2014 Sep 15;106(10):dju237.
doi: 10.1093/jnci/dju237. Print 2014 Oct.

Parity, lactation, and breast cancer subtypes in African American women: results from the AMBER Consortium

Julie R Palmer  1 , Emma Viscidi  2 , Melissa A Troester  2 , Chi-Chen Hong  2 , Pepper Schedin  2 , Traci N Bethea  2 , Elisa V Bandera  2 , Virginia Borges  2 , Craig McKinnon  2 , Christopher A Haiman  2 , Kathryn Lunetta  2 , Laurence N Kolonel  2 , Lynn Rosenberg  2 , Andrew F Olshan  2 , Christine B Ambrosone  2
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Parity, lactation, and breast cancer subtypes in African American women: results from the AMBER Consortium

Julie R Palmer et al. J Natl Cancer Inst. .

Abstract

Background: African American (AA) women have a disproportionately high incidence of estrogen receptor-negative (ER-) breast cancer, a subtype with a largely unexplained etiology. Because childbearing patterns also differ by race/ethnicity, with higher parity and a lower prevalence of lactation in AA women, we investigated the relation of parity and lactation to risk of specific breast cancer subtypes.

Methods: Questionnaire data from two cohort and two case-control studies of breast cancer in AA women were combined and harmonized. Case patients were classified as ER+ (n = 2446), ER- (n = 1252), or triple negative (ER-, PR-, HER2-; n = 567) based on pathology data; there were 14180 control patients. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated in polytomous logistic regression analysis with adjustment for study, age, reproductive and other risk factors.

Results: ORs for parity relative to nulliparity was 0.92 (95% CI = 0.81 to 1.03) for ER+, 1.33 (95% CI = 1.11 to 1.59) for ER-, and 1.37 (95% CI = 1.06 to 1.70) for triple-negative breast cancer. Lactation was associated with a reduced risk of ER- (OR = 0.81, 95% CI = 0.69 to 0.95) but not ER+ cancer. ER- cancer risk increased with each additional birth in women who had not breastfed, with an OR of 1.68 (95% CI = 1.15 to 2.44) for 4 or more births relative to one birth with lactation.

Conclusions: The findings suggest that parous women who have not breastfed are at increased risk of ER- and triple-negative breast cancer. Promotion of lactation may be an effective tool for reducing occurrence of the subtypes that contribute disproportionately to breast cancer mortality.

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Figures

Figure 1.
Figure 1.
Odds ratios for number of births in relation to ER- and ER+ breast cancer, according to lactation history. Reference is women who had only one birth and had breastfed.
Figure 2.
Figure 2.
Odds ratios for parity in relation to breast cancer according to years since last birth. Reference is nulliparous women.
See this image and copyright information in PMC

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