How does fulvestrant work, and who is it for?

Many breast cancers grow in response to the hormone oestrogen. Their cells carry oestrogen receptors, which act like locks on the cell. When oestrogen fits into the lock, it sends a signal that tells the cancer cell to grow and divide. These cancers are called hormone receptor positive, or oestrogen receptor positive. Fulvestrant works directly on the lock. It attaches to the oestrogen receptor, blocks oestrogen from using it and changes the receptor's shape so that the cell breaks it down. With fewer working receptors, the cancer loses an important growth signal. This is why fulvestrant is called a selective oestrogen receptor degrader, or SERD. It works differently from tamoxifen, which blocks the receptor but can still switch it on slightly, and from aromatase inhibitors, which lower the amount of oestrogen the body makes. Fulvestrant is mainly used for hormone receptor positive, HER2-negative breast cancer that has spread or come back and cannot be removed with surgery. It is used after menopause, or before menopause together with treatment that stops the ovaries working. It can be given on its own or with a targeted tablet, such as a CDK4/6 inhibitor. It is not usually used for early breast cancer after surgery.

It blocks and removes the receptor

Fulvestrant does not just block oestrogen. It also leads the cell to destroy the receptor oestrogen needs.

It is for hormone-sensitive cancer

It only helps cancers whose cells have oestrogen receptors, confirmed by tests on the tumour.

It is mostly used for advanced disease

Its main place is in breast cancer that has spread, often alongside a targeted tablet.

Fulvestrant is a well-established treatment, but it is important to be clear about what it offers.

It controls rather than removes cancer

For breast cancer that has spread, fulvestrant aims to slow or stop growth and ease symptoms for as long as possible. It does not make advanced cancer go away permanently.

Cancers can stop responding

Over time, cancer cells may find ways around hormone treatment. When that happens, your oncologist will discuss the next option.

It is not always the first choice

If cancer is growing fast or affecting organs seriously, chemotherapy may be advised first because it tends to act more quickly.

What this page cannot tell you

It cannot tell you whether fulvestrant suits your cancer. That depends on your receptor results, earlier treatment and health, which your oncologist can explain.

Fulvestrant is chosen on the basis of the cancer's biology, not only its stage.

Receptor tests on the tumour

A biopsy sample is stained to see whether oestrogen, progesterone and HER2 receptors are present. If cancer has spread, a new biopsy is sometimes taken, because receptors can change over time.

Menopause status

Blood hormone tests may be used to confirm menopause, especially after chemotherapy stopped periods.

Gene tests

Tests for changes such as PIK3CA or ESR1 help decide which medicine to pair with, or use instead of, fulvestrant.