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

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

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • African Americans / statistics & numerical data*
  • Aged
  • Breast Neoplasms / chemistry*
  • Breast Neoplasms / epidemiology
  • Breast Neoplasms / ethnology*
  • Breast Neoplasms / prevention & control
  • Female
  • Humans
  • Lactation*
  • Logistic Models
  • Middle Aged
  • Odds Ratio
  • Parity*
  • Prevalence
  • Receptors, Estrogen / analysis*
  • Risk Factors
  • Surveys and Questionnaires
  • Triple Negative Breast Neoplasms / ethnology
  • United States / epidemiology

Substances

  • Receptors, Estrogen