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Past breast-feeding may decrease risk for breast cancer recurrence, death
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Previous breast-feeding was linked to reduced risks for disease recurrence and breast-cancer death in women with breast cancer, according to study results.
Women who breast-fed were more likely to be diagnosed with the luminal A subtype of breast cancer, and the association between prior breast-feeding and improved prognosis was only significant among women with this subtype, results showed.
“This is the first study we are aware of that examined the role of breast-feeding history in cancer recurrence and by tumor subtype,” Marilyn L. Kwan, PhD, of the division of research at Kaiser Permanente Northern California, said in a press release. “Women who breast-fed are more likely to get the luminal A subtype of breast cancer, which is less aggressive, and breast-feeding may set up a molecular environment that makes the tumor more responsive to anti-estrogen therapy.”
Kwan and colleagues evaluated data from 1,636 women enrolled in the Life After Cancer Epidemiology (LACE) and Pathways prospective cohort studies. The mean time from diagnosis to enrollment was 23 months among women in the LACE study and 1.8 months among women in the Pathways study.
Researchers used the PAM50 gene expression assay to determine tumor subtype (luminal A, luminal B, HER-2–enriched or basal-like), and they established patients’ breast-feeding history through a questionnaire.
Overall, 882 women indicated that they breast-fed at any point and 754 women indicated that they never breast-fed.
Median follow-up was 9 years.
Researchers observed 383 documented recurrences, 551 overall deaths and 290 breast cancer-related deaths.
Women with the luminal A breast cancer subtype — a majority of whom were diagnosed with early-stage disease — were more likely to have breast-fed than patients with the basal-like subtype (OR = 0.56; 95% CI, 0.39-0.8).
Models adjusted for factors such as age at diagnosis, race/ethnicity, stage and disease subtype indicated breast-feeding at any point was associated with a decreased risk for recurrence in all women (HR = 0.7; 95% CI, 0.53-0.93), especially among women who breast-fed for 6 months or longer (HR = 0.63; 95% CI, 0.46-0.87). Ever breast-feeding also was associated with improved breast-cancer specific mortality (HR = 0.72; 95% CI, 0.53-0.93), which again was more apparent among women who breast-fed for 6 months or longer (HR = 0.61; 95% CI, 0.43-0.88).
Data stratified by disease subtype indicated only women with luminal A tumors who breast-fed displayed significantly reduced risks for recurrence (HR = 0.52; 95% CI, 0.31-0.89) and breast cancer-specific mortality (HR = 0.52; 95% CI, 0.29-0.93).
The researchers acknowledge the need for a larger cohort of women with basal-like tumors to evaluate a potential link between breast-feeding and improved outcomes in this rare tumor subtype.
“Further replication studies are needed to understand the underlying biological mechanisms by intrinsic subtype,” Kwan and colleagues concluded. “However, it is both intriguing and plausible that prior breast-feeding leads to increased differentiation of breast luminal cells via GATA-3 expression, which can predetermine a luminal A tumor with better prognosis and improved response to anti-estrogen therapy. Our findings not only lend further support to the established benefits of breast-feeding but also provide new insight into the mechanistic intricacies of lactation on breast cancer prognosis.” – by Cameron Kelsall
Disclosure: Kwan reports no relevant financial disclosures. One study researcher reports financial interest in Bioclassifier LLC and University Genomics.
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