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J Natl Cancer Inst. 2015 Apr 28;107(7). pii: djv087. doi: 10.1093/jnci/djv087. Print 2015 Jul.

Breastfeeding, PAM50 tumor subtype, and breast cancer prognosis and survival.

Author information

1
Division of Research, Kaiser Permanente Northern California, Oakland, CA (MLK, CHK, LAH, EKW, AC, EPG, CPQJr, LHK, BJC); Huntsman Cancer Institute, University of Utah, Salt Lake City, UT (PSB, REF, IJS, CS); Associated Regional and University Pathologist Institute for Clinical and Experimental Pathology, Salt Lake City, UT (PSB, REF); Division of Epidemiology, Department of Internal Medicine, School of Medicine, University of Utah, Salt Lake City, UT (KSM, CS); Department of Preventive Medicine, University of Southern California, Los Angeles, CA (BML). marilyn.l.kwan@kp.org.
2
Division of Research, Kaiser Permanente Northern California, Oakland, CA (MLK, CHK, LAH, EKW, AC, EPG, CPQJr, LHK, BJC); Huntsman Cancer Institute, University of Utah, Salt Lake City, UT (PSB, REF, IJS, CS); Associated Regional and University Pathologist Institute for Clinical and Experimental Pathology, Salt Lake City, UT (PSB, REF); Division of Epidemiology, Department of Internal Medicine, School of Medicine, University of Utah, Salt Lake City, UT (KSM, CS); Department of Preventive Medicine, University of Southern California, Los Angeles, CA (BML).

Abstract

BACKGROUND:

Breastfeeding is associated with decreased breast cancer risk, yet associations with prognosis and survival by tumor subtype are largely unknown.

METHODS:

We conducted a cohort study of 1636 women from two prospective breast cancer cohorts. Intrinsic tumor subtype (luminal A, luminal B, human epidermal growth factor receptor 2 [HER2]-enriched, basal-like) was determined by the PAM50 gene expression assay. Breastfeeding history was obtained from participant questionnaires. Questionnaires and medical record reviews documented 383 recurrences and 290 breast cancer deaths during a median follow-up of nine years. Multinomial logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) between breastfeeding and tumor subtype. Cox regression was used to estimate hazard ratios (HRs) for breast cancer recurrence or death. Statistical significance tests were two-sided.

RESULTS:

Breast cancer patients with basal-like tumors were less likely to have previously breastfed than those with luminal A tumors (OR = 0.56, 95% CI = 0.39 to 0.80). Among all patients, ever breastfeeding was associated with decreased risk of recurrence (HR = 0.70, 95% CI = 0.53 to 0.93), especially breastfeeding for six months or more (HR = 0.63, 95% CI = 0.46 to 0.87, P trend = .01). Similar associations were observed for breast cancer death. Among women with luminal A subtype, ever breastfeeding was associated with decreased risks of recurrence (HR = 0.52, 95% CI = 0.31 to 0.89) and breast cancer death (HR = 0.52, 95% CI = 0.29 to 0.93), yet no statistically significant associations were observed among the other subtypes. Effects appeared to be limited to tumors with lower expression of proliferation genes.

CONCLUSIONS:

History of breastfeeding might affect prognosis and survival by establishing a luminal tumor environment with lower proliferative activity.

PMID:
25921910
PMCID:
PMC4554253
DOI:
10.1093/jnci/djv087
[Indexed for MEDLINE]
Free PMC Article

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