Breast Feeding and Breast Cancer
For most of us, this is a distant issue, but I am really struck by this recent study. For years, breast feeding has been on the list of "Do"s to reduce one's risk of breast cancer. Presumably, that is because of the reduction of estrogen while nursing--and probably about as reliable as "you can't get pregnant while you are nursing." I do vividly remember reading and hearing both things and nursed both my daughters for more than a year. Now this. Note that the study states that nursing does not impact the risk of developing breast cancer, but seems to suggest that women who do nurse for more than six months are more likely, if they do get breast cancer, to have more aggressive versions.
EBCC: Longer Breastfeeding Linked to Aggressive Tumors
By Charles Bankhead, Staff Writer, MedPage Today
March 28, 2010
BARCELONA -- A longer duration of breastfeeding may predispose women who develop breast cancer to a more aggressive case, but they're no more likely to develop the disease in the first place, findings from a large Swedish cohort study suggest.
Among women who developed breast cancer after pregnancy, those who breastfed their children for more than six months had a twofold increased risk of grade III (high-grade) cancers and tumors with high levels of the proliferation marker Ki-67. However, duration of breastfeeding did not influence a woman's risk of developing breast cancer,
Salma Butt, MD, said during a press briefing at the European Breast Cancer Conference. "We conclude that there is no association between breastfeeding and the risk of breast cancer," said Butt, of Malmo University Hospital. "We also conclude that high duration of breastfeeding is associated with more aggressive breast cancer subgroups."
"Since this is an epidemiological study, you can't really establish any causal relationship, which is very important to remember," she added.
Multiple studies have shown that breastfeeding reduces the risk of breast cancer. But researchers didn't know whether the protective effect extends to tumor aggression, Butt said. To examine the issue,
investigators analyzed data from a prospective cohort study involving 14,092 women followed for an average of 10 years. During that time, 424 breast cancers were diagnosed.
Butt and colleagues classified the tumors on the basis of invasiveness, proliferation (Ki-67 values), HER2 status, the cell-cycle proteins p27 and cyclin D1, Nottingham grade, World Health Organization
breast cancer classification, and hormone receptor status.
Cancer patients were stratified into quartiles of mean breastfeeding duration per child:
>2.2 <4.0 months
>4.0 <6.2 months
The overall risk of breast cancer did not differ across the quartiles of breastfeeding duration. Comparing the highest and lowest breastfeeding quartiles, investigators found that the longer duration
of breastfeeding was associated with an almost a twofold increased risk of grade III breast cancer (HR 1.87, 95% CI 1.05-3.34). The longest duration of breastfeeding more than doubled the incidence of tumors with high levels of Ki-67 (HR 2.15, 95% CI 1.14-4.05).
Longer duration of breast feeding was associated with nonsignificant increases in tumors with elevated cyclin D1 expression and with estrogen receptor-negative tumors and with lower levels of the tumor
The results did not change appreciably in analyses of total time of breastfeeding and time related to the first child.
Butt emphasized that the results should not be considered definitive and that additional studies in other populations are needed to determine more precisely the relationship between breastfeeding duration and breast cancer risk.
Primary source: European Breast Cancer Conference
Butt S et al. "Is duration of breastfeeding related to risk of different breast cancer subgroups?"
EBCC 7. Abstract 503.