Study Finds Link Between Breastfeeding and Lower Risk of Recurrence

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We know that breastfeeding can lower breast cancer risk, especially if you breastfeed for longer than 1 year. This is because:

  • making milk limits breast cells’ ability to act abnormally
  • most women have fewer menstrual cycles when they’re breastfeeding, which means lower estrogen levels
  • many women tend to eat more nutritious food and make healthier lifestyle choices (avoiding alcohol and not smoking) while they’re breastfeeding

A Kaiser Permanente study suggests more benefits for breastfeeding: Women diagnosed with breast cancer who had ever breastfed had a lower risk of the cancer coming back (recurring). The benefits of breastfeeding on recurrence risk were particularly strong for women diagnosed with hormone-receptor-positive, HER2-negative disease.

The study was published in the April 28, 2015 issue of the Journal of the National Cancer Institute. Read the abstract of “Breastfeeding, PAM50 Tumor Subtype, and Breast Cancer Prognosis and Survival.”

In the study, the researchers analyzed tissues samples from breast cancers that had been removed from 1,636 women and classified them as one of four subtypes:

  • luminal A, which is hormone-receptor-positive (either estrogen- and/or progesterone-positive) and HER2-negative; this is the most common type of breast cancer
  • luminal B, which is hormone-receptor-positive (either estrogen- and/or progesterone-positive) and HER2-positive
  • basal-like, which is hormone-receptor-negative and HER2-negative (also called triple-negative breast cancer)
  • HER2-enriched, which is hormone-receptor-negative and HER2-positive

The researchers also reviewed the women’s health records and asked them to complete a questionnaire on breastfeeding.

During the 9 years of follow-up:

  • 383 of the breast cancers came back
  • 290 women died from breast cancer

Overall, women in the study who had ever breastfed had a:

  • 30% lower risk of recurrence
  • 28% lower risk of dying from breast cancer

compared to women who never breastfed.

The benefits were slightly higher for women who breastfed for 6 months or longer.

The researchers also looked to see if breastfeeding offered benefits to women diagnosed with a specific subtype of breast cancer. The results showed:

  • Women diagnosed with triple-negative breast cancer were less likely to have ever breastfed than women diagnosed with hormone-receptor-positive, HER-negative breast cancer.
  • Women diagnosed with hormone-receptor-positive, HER2-negative disease who had breastfed had a 48% lower risk of recurrence and a 48% lower risk of dying from breast cancer compared to women diagnosed with hormone-receptor-positive, HER2-negative disease who didn’t breastfeed.
  • Breastfeeding didn’t seem to affect the outcomes of the other three subtypes of breast cancer.

The researchers said there are a number of reasons why breastfeeding could be linked to a better prognosis if a woman is diagnosed with breast cancer.

“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 [hormonal] therapy,” said Marilyn Kwan, Ph.D., a research scientists with the Kaiser Permanente Division of Research and lead author of the study.

If breastfeeding is an option for you, you may want to consider it. Besides possibly lowering your breast cancer risk and your risk of recurrence if you are ever diagnosed, breastfeeding gives your child antibodies through the breast milk that can protect him/her from bacterial and viral infections. Still, these are highly individual decisions affected by many factors besides breast cancer and recurrence risk and whether you are able to breastfeed.

Breastfeeding can be a challenge after a breast cancer diagnosis. After a double mastectomy, sadly, breastfeeding is impossible. After lumpectomy and radiation, the treated breast usually produces little or no milk, but the other breast usually can make milk normally. The milk from one breast may be enough or you may have to supplement with formula. Some women may choose to use a breast milk donor. An experienced breastfeeding coach can help you figure out the best possible solution for your unique situation.

Still, choosing to breastfeed is a personal decision. For some women, it may be more practical to bottlefeed.

For more information on the benefits of breastfeeding, visit the Breastfeeding History page in the Lower Your Risk section.

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