Little C

Hormone therapy after breast cancer

Tamoxifen, aromatase inhibitors, and what they do

Sources checked: September 2026

The short version

Hormone therapy works by lowering the amount of estrogen in the body or blocking its effect on cancer cells. It's typically recommended for ER-positive or PR-positive cancers and is often taken for several years.

Hormone therapy (sometimes called endocrine therapy) is often recommended for cancers that test -positive or -positive. Rather than killing cells directly the way chemotherapy does, it works by lowering estrogen levels or blocking estrogen's effect on cancer cells.

  • Tamoxifen — blocks estrogen from attaching to receptors on cancer cells; can be used before or after menopause
  • Aromatase inhibitors (such as letrozole or anastrozole) — lower the amount of estrogen the body makes; typically used after menopause
  • Ovarian suppression — reduces estrogen made by the ovaries, sometimes combined with the therapies above

Hormone therapy is often taken for five to ten years. Side effects and the right duration vary by person — your care team can help weigh the options for your situation.

Questions you may want to ask

  • Which hormone therapy are you recommending, and why that one?

  • How long am I likely to be on it?

  • What side effects should I watch for?

Sources

Related articles

Understanding tamoxifenTamoxifen blocks estrogen from attaching to receptors on cancer cells, and can be used before or after menopause.Understanding aromatase inhibitorsAromatase inhibitors lower the amount of estrogen the body makes, and are typically used after menopause.Understanding ovarian suppressionOvarian suppression temporarily stops the ovaries from producing estrogen, sometimes combined with other hormone therapy.Managing menopausal symptoms during treatmentChemotherapy, ovarian suppression, and hormone therapy can all bring on or worsen menopausal symptoms, with care-team-guided ways to manage them.