Women whom were diagnosed with breast cancer and had previously breastfed their babies were 30 percent less likely to have the disease recurring, according to a new Kaiser Permanente research published in the Journal of the National Cancer Institute.
Scientists found that breastfeeding had a protective effect that was more pronounced for some tumors, with particular genetic subtypes, among them being the most common of all breast cancers.
The study focused on 1,636 women with breast cancer who filled out a questionnaire that offered details breastfeeding history. Additional data were obtained from medical reviews and the comprehensive electronic health record Kaiser Permanente HealthConnect.
“This is the first study we’re aware of that examined the role of breastfeeding history in cancer recurrence, and by tumor subtype,” said Marilyn L. Kwan, PhD, research scientist with the Kaiser Permanente Division of Research and lead author of the study.
The researchers discovered the benefits of breastfeeding among women who were diagnosed with the luminal A subtype of breast cancer. On the other hand, no important associations were found for those with other subtypes. Luminal A cancer also include the estrogen-receptor positive (or ER+) tumors – the most common of all breast tumors. This form of cancer is less likely to metastasize. Also, the disease is treatable with hormonal therapy, like aromatase inhibitors and tamoxifen.
Women who breastfed had 28 percent more chances to survive the disease, in addition to lowered risk of breast cancer recurrence.
“Women who breastfeed are more likely to get the luminal A subtype of breast cancer, which is less aggressive, and breastfeeding may set up a molecular environment that makes the tumor more responsive to anti-estrogen therapy,” Kwan said.
Scientists don’t know for certain why women who breastfeed are developing less aggressive tumors.
According to Bette Caan, an author of the study and DrPH, senior research scientist with the Kaiser Permanente Division of Research, breastfeeding is believed to increase the maturation of the breast’s ductal cells, which makes it less exposed to carcinogens or to the excretion of carcinogens, while leading to slower growing tumors.
It is well known that breastfeeding is very beneficial for babies, Kwan added, and the new study is revealing that it also has huge benefits for mothers. “In fact, the protection was even stronger for women who had a history of breastfeeding for 6 months or more.”
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