Breastfeeding and breast cancer risk by receptor status--a systematic review and meta-analysis.
BACKGROUND
Breastfeeding is inversely associated with overall risk of breast cancer. This association may differ in breast cancer subtypes defined by receptor status, as they may reflect different mechanisms of carcinogenesis. We conducted a systematic review and meta-analysis of case-control and prospective cohort studies to investigate the association between breastfeeding and breast cancer by estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) status.


METHODS
We searched the PubMed and Scopus databases and bibliographies of pertinent articles to identify relevant articles and used random-effects models to calculate summary odds ratios (ORs) and 95% confidence intervals (CIs).


RESULTS
This meta-analysis represents 27 distinct studies (8 cohort and 19 case-control), with a total of 36 881 breast cancer cases. Among parous women, the risk estimates for the association between ever (versus never) breastfeeding and the breast cancers negative for both ER and PR were similar in three cohort and three case-control studies when results were adjusted for several factors, including the number of full-term pregnancies (combined OR 0.90; 95% CI 0.82-0.99), with little heterogeneity and no indication of publication bias. In a subset of three adjusted studies that included ER, PR, and HER2 status, ever breastfeeding showed a stronger inverse association with triple-negative breast cancer (OR 0.78; 95% CI 0.66-0.91) among parous women. Overall, cohort studies showed no significant association between breastfeeding and ER+/PR+ or ER+ and/or PR+ breast cancers, although one and two studies (out of four and seven studies, respectively) showed an inverse association.


CONCLUSIONS
This meta-analysis showed a protective effect of ever breastfeeding against hormone receptor-negative breast cancers, which are more common in younger women and generally have a poorer prognosis than other subtypes of breast cancer. The association between breastfeeding and receptor-positive breast cancers needs more investigation.
Surveillance and Health Services Research, American Cancer Society, Atlanta Institute for Translational Epidemiology and the Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York.
F
F
Islami
Division of Public Health Sciences, Department of Surgery, Washington University School of Medicine, St Louis, USA.
Y
Y
Liu
Surveillance and Health Services Research, American Cancer Society, Atlanta.
A
A
Jemal
Institute for Translational Epidemiology and the Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York.
J
J
Zhou
Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden Department of Community Medicine, Faculty of Health Sciences, University of Tromsø, The Arctic University of Norway, Tromsø Cancer Registry of Norway, Oslo, Norway Department of Genetic Epidemiology, Folkhälsan Research Center, Helsinki, Finland.
E
E
Weiderpass
Division of Public Health Sciences, Department of Surgery, Washington University School of Medicine, St Louis, USA Siteman Cancer Center, Washington University School of Medicine, St Louis.
G
G
Colditz
Institute for Translational Epidemiology and the Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York.
P
P
Boffetta
Breastcancer.org/breasthealth.org, Lankenau Medical Center, Wynnewood, USA mweiss@breastcancer.org.
M
M
Weiss
D001942:Breast Feeding / Q000639:trends; D001943:Breast Neoplasms / Q000378:metabolism* / Q000517:prevention & control*; D016022:Case-Control Studies; D015331:Cohort Studies; D005260:Female; D006801:Humans; D011446:Prospective Studies; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis*; D011960:Receptors, Estrogen / Q000096:biosynthesis*; D011980:Receptors, Progesterone / Q000096:biosynthesis*; D012307:Risk Factors
D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; C508053:ERBB2 protein, human
HER2 receptor; breast cancer; breastfeeding; estrogen receptor; meta-analysis; progesterone receptor