How does goserelin work, and who is it for?

Most breast cancers are hormone receptor positive, which means oestrogen can fuel their growth. In women who have not yet reached the menopause, most of that oestrogen comes from the ovaries. The ovaries do not work on their own. They take their orders from the pituitary gland at the base of the brain, which releases two messenger hormones, LH and FSH, in response to a signal called GnRH. Goserelin, also known by the brand name Zoladex, is a man-made version of GnRH. Given as a small implant under the skin of the belly, it releases a steady stream of this signal. At first the pituitary responds by releasing more LH and FSH, so hormone levels can rise for a week or two. Because the signal never switches off, though, the pituitary soon becomes unresponsive and stops sending messages. The ovaries then stop making oestrogen, and levels usually fall to those seen after the menopause within about three to four weeks. As long as the implant is replaced on time, the ovaries stay switched off. This is called ovarian function suppression. Goserelin does not attack cancer cells directly. Instead, it takes away the fuel that hormone-sensitive cancer cells rely on, and makes it possible for other hormone treatments to work well in younger women.

It works through the brain, not the breast

Goserelin quietens the brain signal that drives the ovaries, so the effect reaches the whole body.

It is for hormone receptor positive cancer

If your cancer is hormone receptor negative, lowering oestrogen will not help control it, so goserelin is not used to treat it, although it may still be offered to protect the ovaries during chemotherapy.

The effect is temporary

When the implants stop, the pituitary usually wakes up again and the ovaries can restart, depending on age and past treatment.

Understanding the mechanism helps explain both why goserelin is useful and why it has the effects it does. It also explains some limits that are worth knowing before you start.

It only helps hormone-sensitive cancer

The whole benefit comes from lowering oestrogen. If a cancer does not depend on oestrogen, taking it away will not slow it down.

Side effects come from the same action

Low oestrogen is what treats the cancer, and it is also what causes hot flushes, vaginal dryness, mood changes and bone thinning. The two cannot be fully separated.

Suppression is not always complete

In a small number of women, especially those who are younger or who start an aromatase inhibitor early, the ovaries are not fully switched off. Your team may check blood oestradiol levels to confirm it is working.

What this page cannot tell you

It cannot tell you how much goserelin would lower your own risk, or whether its benefit outweighs its effects for you. That depends on your cancer's features, your age and your wishes, which your oncologist can talk through with you.

There is no single rule. The decision balances the chance of benefit against years of menopause symptoms at a young age.

Your menopause status

Your team needs to know whether your ovaries are still working. After chemotherapy, periods may stop for a while and then return, so blood tests over time can help.

The risk of the cancer returning

The size of the tumour, whether lymph nodes were involved, the grade, and sometimes a genomic test all feed into this estimate. Women at low risk may do well on tamoxifen alone.