Breast cancer and estrogen: check your levels, please

Breast cancer and estrogen

We hear a lot about estrogen. But there are actually three kinds of it: estrone, estriol, and estradiol. When estrogen (particularly estradiol) gets too high, it can cause a number of unwanted symptoms. And, more importantly, it can also raise your risk of estrogen-receptor positive breast cancer.

What causes high estrogen

It’s normal for estrogen to fluctuate throughout a woman’s cycle. However, estrogen can become and stay elevated for a number of reasons. Environmental xenoestrogens (chemicals that mimic estrogen), certain birth control methods, alcohol, low progesterone, and even hormone replacement therapy can all contribute to estrogen levels that are out of balance.

High estrogen in perimenopause

Progesterone is a sex hormone that counters estrogen. While estrogen promotes growth, progesterone is a natural diuretic and has a calming effect. In perimenopause (the years leading up to menopause), your body reduces the amount of progesterone it makes.

The problem is: progesterone starts to decline in your late thirties. But estrogen levels don’t. They may stay the same, or swing up and down wildly. Without enough progesterone to balance it, estrogen (mostly estradiol) becomes the dominant hormone. Sometimes, this can even happen when estradiol lab results appear within limits. The condition is called estrogen dominance.

Some symptoms of high estrogen are:

  • Acne
  • Weight gain
  • Swollen or tender breasts
  • Fibrocystic breasts
  • Frequent or heavy periods
  • Low energy
  • Worsening PMS
  • Trouble remembering things
  • Changes in mood or outlook
  • Water retention
  • Low sex drive

High estrogen in menopause, induced menopause, and postmenopause

When you’ve had your last period—and haven’t had another for 12 consecutive months—you’re in menopause. The ovaries no longer release eggs. Both estrogen and progesterone levels are low. So, how can you have estrogen dominance? Some women use hormone replacement therapy (HRT) to get through the symptoms of menopause. But, if you’re supplementing with estrogen, know this: it’s possible for levels to get too high and cause problems.

How high estrogen is linked to breast cancer

Sure, it causes some seriously uncomfortable symptoms. But why is high estrogen so important to keep an eye on? Nearly 80% of breast cancers are estrogen-receptor positive (ER-positive). That means cancer cells attach to estrogen. The estrogen enables them to grow and thrive.

For many years, research framed estrogen-receptor positive breast cancer as a postmenopausal condition. And, while it’s true younger women are more likely to deal with hormone-receptor negative breast cancer, ideas about ER-positive cancer—and who it affects—are changing.

Several years ago, the Endogenous Hormones and Breast Cancer Collaborative Group set out to re-evaluate and re-analyze individual data from seven studies. They looked for an association between hormones and breast cancer in younger women. More studies are still needed, but they came to a conclusion. Estrogen can raise the risk of ER-positive breast cancer, even before menopause.

Monitoring your estrogen levels

No matter what stage of life you’re in, talk with your healthcare provider. It’s important to monitor hormones, especially if you’re having symptoms of high estrogen.

Estrogen levels are easy to check. Labs can report on total estrogen. They can also break down results by estrogen type. This will let you take a closer look at your estradiol. 

It’s also good to check progesterone. Your levels may be too low and contributing to estrogen dominance. Or, your progesterone could be too high. And, you don’t want that, either. About 65% of estrogen-receptor positive breast cancers are also progesterone-receptor positive (PR-positive). That means they can grow by attaching to progesterone, too.

Other thoughts

It’s important to remember that estrogen isn’t the only factor that increases risk of breast cancer. About 10–20% of breast cancers are triple-negative and don’t need estrogen or progesterone to grow. Some examples are HER2-positive breast cancers and those related to the BRCA1 gene.