A large study has found that breastfeeding -- even for a short time -- is associated with up to a 20% lower risk of developing hormone-receptor-negative breast cancer.
Marisa Weiss, M.D., Breastcancer.org chief medical officer, is a main author of the study. The research was a collaboration between Breastcancer.org, the Icahn School of Medicine at Mount Sinai, Washington University, and the American Cancer Society.
The research was published online on Oct. 26, 2015 by the Annals of Oncology. Read the abstract of “Breastfeeding and breast cancer risk by receptor status -- a systematic review and meta-analysis.”
Other studies also have shown that breast cancer risk is lower among women who have breastfed. Still, few studies have looked at links between breastfeeding and a lower risk of particular types of breast cancer.
Hormone-receptor-negative breast cancers have no receptors for the hormones estrogen or progesterone. This subtype of breast cancer doesn’t respond to hormonal medicines, such as tamoxifen or the aromatase inhibitors, which target hormone receptors. Hormone-receptor-negative breast cancer is considered more aggressive than hormone-receptor-positive breast cancer. This breast cancer subtype is more likely to be diagnosed in women:
- younger than 50
- who are Black
- who have had multiple pregnancies at a young age
- with an abnormal BRCA1 gene
In the United States, about 20% of breast cancer is hormone-receptor-negative. Most hormone-receptor-negative breast cancers also have no receptors for the HER2 protein, which makes them “triple negative.”
This study was a meta-analysis. A meta-analysis combines and analyzes the results of a number of earlier studies. In this case, results from 27 studies looking at breastfeeding and breast cancer risk were in the meta-analysis. The studies included nearly 37,000 cases of breast cancer and more than 790,000 women. The studies were published between 1983 and 2014.
The researchers looked to see whether the women had ever breastfed. They also looked at the characteristics of the breast cancers that were diagnosed in the studies.
The researchers found that women who had breastfed for any amount of time had up to a 20% lower risk of hormone-receptor-negative breast cancer.
“Further evidence to support the long-term protection of breastfeeding against the most aggressive subtypes of breast cancer is very encouraging and actionable,” said Dr. Weiss. “Breastfeeding is a relatively accessible, low-cost, short-term strategy that yields long-lasting natural protection.
“This work highlights the need for more public health strategies that directly inform women and girls about the maternal -- and fetal -- benefits of breastfeeding before and during a woman’s child-bearing years,” Dr. Weiss continued. “It’s also important for these women to have the message reinforced by their doctors.”
If you will be having children and breastfeeding is an option for you, you may want to consider it. Besides possibly lowering your risk of hormone-receptor-negative breast cancer, breastfeeding also provides many benefits to your child. Still, these are highly individual decisions affected by many factors besides breast cancer risk and whether you are able to breastfeed.
If you’ve had breast cancer and plan to have children, breastfeeding may no longer be an option if you’ve had a double mastectomy. Some women who have had lumpectomy and radiation can still make some milk, but the amount is usually small. But the other unaffected breast usually can make enough milk to feed the baby. Still, if the amount of milk is too low, you may have to supplement with bottle feeding.
Even if you are able to breastfeed, choosing to breastfeed is a personal decision. For some women, it may be more practical to bottlefeed. Still, if you’re considering whether to breastfeed or not, you may want to talk to your doctor about this study. Your doctor or someone in your doctor’s office can give you much more information on breastfeeding and its benefits and refer you to a lactation consultant if you have problems.
“If you already did breastfeed and you were diagnosed with a hormone-receptor-negative breast cancer, reading this article may make you feel upset and think, ‘I breastfed and it still happened to me,’” said Dr. Weiss. “Also, some women who have never had breast cancer may be unable to breastfeed or may have great difficulty with breastfeeding. And, some of you reading this article never had the chance to have children and breastfeed. In each of these situations, it’s normal to get upset and frustrated when you read an article like this.
“But it’s important to know that breastfeeding is only one of many things women can do to lower their risk of breast cancer,” she continued. “No one action step provides full protection. In this study, women who breastfed had up to a 20% lower risk of developing breast cancer (it wasn’t 100% prevention). To lower our risk of ever getting breast cancer in the first place or to reduce the risk of recurrence after a diagnosis, the goal is to take a number of steps, day to day, over time. If you are passing this Research News story to loved ones, also tell them about Breasthealth.org, a new place to go for women and girls who are interested in breast cancer prevention.”
Breastfeeding is just one of many things women can do to lower their risk of breast cancer. For more information on steps you can take to keep your risk of breast cancer -- or breast cancer recurrence if you’ve been diagnosed -- as low as it can be, visit the Breastcancer.org Lower Your Risk pages.