Women who breastfeed appear to have lower risk of inherited breast cancer


Women who breastfeed appear to have lower risk of inherited breast cancer

Researchers in the US who analyzed data from a large study of premenopausal women found that breastfeeding was linked to a lower risk of developing the inherited form of the disease. They said their findings lend support to the idea that women with a family history of breast cancer should be encouraged to breastfeed.

The study was the work of lead author Dr Alison M. Stuebe and colleagues and was published online on 10 August in the Archives of Internal Medicine. At the time of the study Stuebe was with Brigham and Women's Hospital and Harvard Medical School, Boston, and has since moved to a new post at the University of North Carolina at Chapel Hill.

Stuebe and colleagues wrote in their background information that more women worldwide develop breast cancer than any other malignancy, and that the risk factors for the disease include having a family history, starting to have periods younger than usual, not having children, or delaying having a first child until late in life.

They decided to do the study because while findings from observational studies suggest there is a link between lactation and premenopausal breast cancer risk, there is no evidence from prospective studies following a large cohort of women.

For this research they used information from the well established and recognized Nurses' Health Study II. The data they used covered 60,075 women who had given birth to at least one live baby (parous) and were followed between 1997 and 2005.

Each participant completed a detailed questionnaire that asked about their demographic characteristics, body measurements and lifestyle, and then filled in further questionnaires every two years.

Breastfeeding history was assessed in detail on the questionnaire filled in at the start of the study in 1997. After that, at each follow up, the women were asked to report whether they had received a breast cancer diagnosis.

The researchers then counted the number of premenopausal breast cancer cases that arose in the cohort over that period, and compared the figures for women who had ever breastfed and against those who had not.

The results showed that:

  • There were 608 cases of premenopausal breast cancer during a total of 357,556 person-years of follow-up.
  • Women who had ever breastfed had a 25 per cent lower risk of developing premenopausal breast cancer compared with women who had never breastfed.
  • The risk appeared to be unaffected (ie there was no linear trend) by duration of breastfeeding, whether breastfeeding was exclusive or used with formula, or whether it was accompanied by lack of mestruation (lactation amenorrhea).
  • Family history of breast cancer had a significant effect on the relationship between breastfeeding and premenopausal breast cancer risk.
  • Among women with a first degree relative (parent, sibling, offspring) with breast cancer, those who had ever breastfed had a 59 per cent lower risk of developing premenopausal breast cancer compared with women who had never breastfed.
  • No such link was observed among women without a family history of breast cancer.
Stuebe and colleagues concluded that:

"In this large, prospective cohort study of parous premenopausal women, having ever breastfed was inversely associated with incidence of breast cancer among women with a family history of breast cancer."

They also wrote that:

"Future studies of interactions among breastfeeding history, family history and genotypes associated with breast cancer risk will be needed to confirm these associations and explore underlying mechanisms."

"Moreover, breastfeeding is associated with multiple other health benefits for both mother and child. These data suggest that women with a family history of breast cancer should be strongly encouraged to breastfeed," they added.

The researchers also found that women who did not breastfeed but used drugs to suppress breast milk production also seemed to have a lower risk of breast cancer than women who neither breastfed nor used breast milk suppression.

The authors said this connection could be due to disordered involution, or a fault in the way that mammary tissue returns to its pre-pregnant state caused by engorgement and inflammation.

"Lactation and Incidence of Premenopausal Breast Cancer: A Longitudinal Study."

Alison M. Stuebe; Walter C. Willett; Fei Xue; Karin B. Michels.

Arch Intern Med. 2009;169 (15):1364-137.

Published online 10 August 2009.

Additional source: JAMA and Archives Journals.

Breast Feeding And Breast Cancer Relationship (Video Medical And Professional 2020).

Section Issues On Medicine: Women health