Does hormone therapy work for all breast cancers?

No. Hormone therapy only works for breast cancers that are hormone receptor positive.

To know whether hormone therapy could help, doctors test tumor tissue for proteins called hormone receptors — estrogen receptors (ERs) and progesterone receptors (PRs). If the cancer cells contain these receptors, the cancer is called hormone receptor positive (HR positive). Tumors that lack them (HR negative) do not respond to hormone therapy.

The test runs on tissue taken by surgery or biopsy. The result appears on your pathology report. It is not a blood test, and no scan can show it.

Think of a hormone receptor as a docking point on a cell. Estrogen fits into it. That connection tells the cell to grow. A cancer built with those docking points needs a steady estrogen supply. A cancer without them does not care how much estrogen is around. In that tumor, hormone therapy has nothing to act on.

About 80% of people diagnosed with breast cancer have HR-positive cancers, so hormone therapy is an option for many people, but not everyone.

Hormone therapy works by blocking the body's ability to make hormones or by blocking the effects of hormones on breast cancer cells. Those are two different strategies, and they use different drugs. Aromatase inhibitors cut estrogen production. They include anastrozole, letrozole, and exemestane. Tamoxifen works at the receptor instead, as a selective estrogen receptor modulator. Fulvestrant is a selective estrogen receptor degrader. Goserelin and leuprolide suppress the ovaries.

Menopausal status changes which of these fits. Aromatase inhibitors are used mainly in women past menopause. A premenopausal woman can still take one. But it has to be paired with a drug that suppresses ovarian function. This point confuses many people. It also explains why two people with similar tumors get different prescriptions.

Time is part of how this treatment works. Taken for 5 years or more, hormone therapy can greatly reduce the risk of a new breast cancer. That is a long stretch. Side effects are the main reason people stop early. The most common ones are hot flashes, night sweats, and loss of interest in sex.

Stopping quietly gives up the benefit. Report the side effect instead. Then ask whether a different drug in the same family might suit you better.

If your cancer is HR negative, your care team will recommend other treatments that fit your situation. Chemotherapy is often one of them, along with treatments matched to other features of the tumor.

Look for two lines on your pathology report: estrogen receptor and progesterone receptor. Then ask three questions. Which drug am I taking, and why that one? How long am I meant to take it? And what should I do if the side effects become hard to live with?