Understanding hormone therapy

Hormone therapy (also known as endocrine therapy) is a treatment for breast cancers that are hormone receptor-positive. This means the breast cancer cells have receptors (proteins) that attach to oestrogen and progesterone, which helps them grow.

Hormone therapy stops these hormones from attaching to the receptors. Different hormone therapy drugs do this in different ways.

- By lowering oestrogen levels in the body, or:

- Blocking oestrogen from helping breast cancer cells grow.

Hormone therapy can reach cancer cells almost anywhere in the body, not just in the breast.

Hormones are substances that function as chemical messengers in the body. They affect the actions of cells and tissues in the body (through the bloodstream at various locations in the body).

The hormones oestrogen and progesterone are produced by the ovaries in pre-menopausal women and by other tissues - including fat and skin - in both pre-menopausal and post-menopausal women (drop box when menstrual periods have stopped permanently) and men.

Oestrogen and progesterone promote the development and maintenance of the female reproductive system.

Breast cells contain special proteins called hormone receptors, these hormone receptors are known as oestrogen receptors and progesterone receptors.

When oestrogen receptors are positive (ER+) they can help breast cancers to grow (the cancer cells may receive signals from oestrogen that tell the cells to grow).

Positive progesterone receptors (PR+) may also affect how some breast cancers grow (the cancer cells may receive signals from progesterone that tell them to grow).

Breast cancers that contain oestrogen and/or progesterone receptors are often referred to as hormone receptor-positive. Most ER+ breast cancers are also PR+.

Breast cancers that lack oestrogen are called ER negative (ER-), and if they lack both ER and PR are called hormone receptor-negative.

Approximately 70 to 75% of breast cancers in women in Aotearoa New Zealand are ER+.