Hormones help control how cells grow and what they do in the body. The hormones oestrogen and progesterone, particularly oestrogen, can encourage some breast cancers to grow.
Hormonal therapies reduce the amount of oestrogen in the body or stop it attaching to the cancer cells. They only work for women who have oestrogen-receptor (ER) positive cancers.
Hormonal therapies are commonly prescribed for women with invasive breast cancer. This is because they reduce the risk of breast cancer coming back. Hormonal therapies are also used to treat DCIS, but the benefits of treatment are small.
You may have hormonal therapy before surgery to shrink DCIS. This means you may be able to have breast-conserving surgery instead of a mastectomy. If you are not able to have an operation to remove the cancer, you may have hormonal therapy as your only treatment.
Your cancer doctor may talk to you about the possible benefits and disadvantages of taking hormonal therapy in your situation. The type of hormonal therapy you have depends on whether you have been through menopause or not.
Trials have shown that a hormonal therapy called tamoxifen may reduce the risk of ER positive DCIS coming back. It can also reduce the risk of invasive cancer in both breasts.
It can be used whether you have been through menopause or not. Tamoxifen is taken daily as a tablet, usually for 5 years.
The side effects are similar to the effects of the menopause and may include:
- hot flushes and sweats
- weight gain
For women who have been through the menopause, tamoxifen can slightly increase the risk of womb (endometrial) cancer. It can also increase the risk of developing a blood clot. Although this sounds frightening, these effects are very rare. If they happen, they are usually found very early when they can be successfully treated.
Aromatase inhibitors (AIs)
Aromatase inhibitors (AIs) are the main hormonal therapy used for women with invasive breast cancer after the menopause. They stop oestrogen being made in the fatty tissue.
Like tamoxifen, these drugs only work if you have an ER positive DCIS.
If you have been through the menopause and have ER positive DCIS, trials have shown that AIs may reduce the risk of:
- DCIS coming back
- developing an invasive cancer in both breasts.
You may have AIs for 3 to 6 months before surgery. The aim is to shrink the DCIS so that you can have breast-conserving surgery instead of a mastectomy.
Your cancer doctor or specialist nurse can tell you more about any trials that you may be suitable for.
Your doctor may prescribe an aromatase inhibitor such as:
These drugs are taken daily as a tablet. Side effects can include:
- joint and muscle pain
- hot flushes.