Hormones and Breast Cancer: What You Should Know

New Research Again Links Increased Breast Cancer Risk to Longer Use of Hormone Therapy.

The link between hormone therapy and breast cancer has been recognized for years. But an analysis published Aug. 29, 2019, in The Lancet has added some additional information to the discussion. The analysis looked at 58 studies that included information on the type and timing of hormone use in individual women, and their body mass index. Researchers began gathering the studies in 1992 and continued until 2018.

We asked Dr. Wendy Chen, an assistant professor of medicine at Harvard Medical School, to help us sort through both the old and new information on hormone use and breast cancer and what it means for women considering starting hormone therapy.

What's the connection between hormone therapy and breast cancer?

It's been known, and this study appeared to confirm, that women who take hormone therapy for a longer amount of time have a higher risk of developing invasive breast cancer than women who use the treatments for a shorter period. Risk continues to increase over time and does not plateau, says Dr. Chen.

Unlike past studies, such as the Women's Health Initiative, which found that breast cancer risk started to rise only after two to three years of hormone use, the Lancet study found that breast cancer risk rose almost immediately when a woman started hormone therapy. But that observation may be due to imprecise information about the duration of hormone therapy in some of the data that the study authors used for their analysis, says Dr. Chen. It's reasonable to say that risk of breast cancer starts to rise a year or so after starting hormone therapy and continues to climb from there.

Is there a difference in cancer risk depending on the type of therapy a woman uses?

Yes. In the Lancet study, while both estrogen-only therapies and progesterone-estrogen combinations elevated the risk of breast cancer, risk was higher in women who took the combination treatments. The Lancet study also found that the risks of estrogen-only therapy appear to be higher in normal-weight women compared with obese women. This may be the case because women with obesity already have higher breast cancer risk because they have higher levels of estrogen in their blood. "I'm still not comfortable saying that if you are overweight you don't have to worry about taking hormones," says Dr. Chen.

Women with obesity had the same elevated risk as normal-weight women when taking estrogen-progesterone combination therapies.

Does vaginal estrogen also raise the risk of breast cancer?

This study confirmed that vaginal estrogen treatments don't appear to raise the risk of breast cancer. "It's unlikely that vaginal estrogens would be associated with a large increase in breast cancer risk," says Dr. Chen.

Does hormone therapy bring greater risks if it's started at a younger age?

The study seems to indicate that this is the case, but there's reason to question that conclusion. Younger women in this study generally took hormones for a longer period of time. So, risk appears to relate more to the duration of use than to the age a woman started taking hormone therapy.

Do the breast cancer risks related to hormone therapy go away once you stop taking hormones?

No. The risk of breast cancer related to hormone use remains high years after hormone therapy stops.

Based on all this information, should women take hormones to manage menopausal symptoms?

"The bottom line is that if someone wants to use hormone therapy for a few years to manage menopause symptoms, that's still reasonable to do in most cases," says Dr. Chen. But ideally, women should only take hormones for as short a time as possible. "In general, what I say to patients is to use nonhormonal strategies first," says Dr. Chen.

If nonhormonal strategies aren't working and your symptoms are mainly vaginal, consider a vaginal estrogen. Someone who has multiple symptoms, such as hot flashes, night sweats, and vaginal symptoms, could consider hormone therapy with a pill or patch if other strategies fail and symptoms are truly bothersome.

In addition, hormones should only be used if medically indicated. Many people mistakenly believe that using hormones will make them look younger or extend their life span. It won't.

How long is too long when it comes to hormone therapy?

"Five years is really the outer limit for hormone use. Ideally it should be for a year or two at the most, and it should be directed toward addressing symptoms," says Dr. Chen. If you do opt for hormones, be certain to taper off rather than stopping them abruptly when you are ready to discontinue treatment. Women who stop hormone therapy suddenly may experience a resurgence in symptoms.