Doctors may prescribe estrogen inhibitors, also known as aromatase inhibitors, to treat early stage hormone receptor-positive (HR-positive) breast cancer in postmenopausal people.

These medications also help treat HR-positive breast cancer that has metastasized (spread). Doctors may use them alongside other treatments, such as chemotherapy and surgery.

HR-positive breast cancers require estrogen to grow. Before menopause, most estrogen comes from the ovaries.

During menopause, estrogen levels decline. However, people may still have small amounts of this hormone due to an enzyme called aromatase, which turns androgen hormones into estrogen.

Aromatase inhibitors do not stop the ovaries from producing estrogen, but they stop aromatase from working.

Therefore, doctors will typically only prescribe these medications to postmenopausal people. They may also recommend them for individuals whose ovaries are not producing estrogen for another reason, such as those taking ovarian suppression medications.

By lowering estrogen levels, aromatase inhibitors may help slow or prevent HR-positive breast cancer.

Estrogen inhibitors for breast cancer include the following:

These medications typically come in tablet form, and a person may need to take them daily. Treatment duration can be as long as 10 years and will depend on an individual’s circumstances.

According to the American Cancer Society, aromatase inhibitors may cause the following side effects:

People may also experience ulcers, blisters, allergic reactions, and liver inflammation.

If someone experiences these side effects, their healthcare team may switch them to a different aromatase inhibitor, stop the treatment, or manage the side effects with other medications.

Aromatase inhibitors may also help prevent breast cancer. Research suggests that exemestane and anastrozole may reduce the risk of breast cancer in postmenopausal people with a higher than average risk.

Another treatment and prevention option that a doctor may suggest is tamoxifen (Nolvadex). This medication is a selective estrogen receptor modulator that is particularly effective at treating ER-positive breast cancer.

HR-positive breast cancers tend to grow more slowly than HR-negative breast cancers, but prompt treatment is still important.

People with any signs of breast cancer need to speak with a healthcare professional for diagnosis and to discuss their potential treatment options.

Those who may have a higher risk of these cancers, such as individuals with a family history of HR-positive breast cancer, can also discuss prevention with a healthcare professional.