A recent study published in the Journal of the National Cancer
Institute, suggests that breastfeeding may correlate with better prognosis and survival in patients with a certain intrinsic subtype of breast cancer. ”The results of this study are likely to be another factor in clinicians’ discussions about whether new (or soon to be) mothers decide to breastfeed,” Professor Marilyn L. Kwan (Kaiser
Permanente Research Division) noted in an email. A woman’s history of breastfeeding may influence her prognosis and survival by establishing a ductal tumor environment with lower proliferative activity. According to the researchers, “Our findings not only further support the benefits of breastfeeding, but also provide new insights into the complex mechanisms of breastfeeding on breast cancer prognosis.” Two prospective cohort studies had 1636 breast cancer survivors, and Professor Kwan and colleagues applied PAM50 gene expression analysis to determine the intrinsic tumor subtype (ductal A, ductal B, human epidermal growth factor receptor 2 enriched, or basal-like). They obtained breastfeeding history from the questionnaire. During a median follow-up of 9 years, 383 patient breast cancer recurrences and 290 patient deaths were recorded in medical cases. Using multinomial logistic regression, the researchers assessed the ratio between breastfeeding and tumor subtype. With the help of Cox regression, they assessed the risk ratio for breast cancer recurrence or death. Tubular A tumors tended to have the best prognosis of the four molecular subtypes, and patients with basal-like breast cancer were the least likely to have a history of breastfeeding compared to tubular A tumors (OR=0.56). Among all patients, a history of breastfeeding was associated with a lower risk of recurrence (HR=0.70), especially breastfeeding for 6 months or longer (HR=0.63, p-value for trend=0.01). The factors associated with death from breast cancer were similar. In female patients with ductal A subtype, a history of breastfeeding was associated with a reduced risk of recurrence (HR=0.52) and death (HR=0.52), but the authors found no significant association between the other subtypes. “This effect appears to be limited to lower proliferative gene expression tumors,” the researchers described. There may be better efficacy in ductal B and basal-like tumors, but the correlation was not significant. ”Few studies have examined whether a history of breastfeeding has an effect on breast cancer recurrence, and whether that effect varies with the type of initial tumor diagnosis,” Professor Kwan noted. “Breastfeeding has been shown to have the potential to lead to a reduced risk of breast cancer through hormonal mechanisms. Therefore, the potential protective effect of breastfeeding on breast cancer recurrence seems reasonable.”