Endometrial monitoring and bleeding on tamoxifen

Tamoxifen blocks oestrogen in breast tissue, but in the womb it acts a little like oestrogen. In women who have been through menopause, this can make the lining of the womb, the endometrium, thicker and can occasionally lead to polyps, overgrowth of the lining, or, rarely, womb cancer. The risk of womb cancer is small, and for most women the benefit of tamoxifen in preventing breast cancer recurrence is far greater. The most important step is to report any unusual vaginal bleeding promptly, because it can be checked and treated early.

Who is most affected

The effect on the womb matters mainly for postmenopausal women. In premenopausal women, the risk of womb cancer on tamoxifen is not clearly raised.

Routine scans are not usually needed

Tamoxifen commonly makes the lining look thicker on ultrasound, even when nothing is wrong. Routine scans in women without symptoms tend to lead to unnecessary procedures, so most guidelines advise investigating symptoms rather than scanning everyone.

What needs checking

Any vaginal bleeding or spotting after menopause, bleeding between periods or after sex, unusual discharge, or pelvic pain should be reported so the womb can be assessed.

The possibility of womb cancer can make tamoxifen feel frightening. It helps to keep the numbers in proportion. For most women, especially those with hormone-sensitive breast cancer, the reduction in breast cancer recurrence from tamoxifen is much larger than the small increase in womb cancer risk.

Womb cancers are usually found early

Womb cancer on tamoxifen usually causes bleeding early, which is why reporting bleeding matters so much. When found early, it is often treated successfully with surgery.

Switching can remove the concern

For postmenopausal women, an aromatase inhibitor does not affect the womb in this way. If womb changes are a concern, your oncologist may discuss switching.

A thick lining on a scan is not a diagnosis

Many women on tamoxifen have a lining that looks thick without any disease. Decisions are based on symptoms and further tests, not the scan alone.

What this page cannot tell you

It cannot tell you your own risk. Ask your team how it applies to you.

For women who still have periods, tamoxifen can make them irregular, lighter, heavier or stop altogether, which can be confusing.

Changes in periods

Irregular periods are common on tamoxifen and are not usually a cause for concern, but very heavy or prolonged bleeding should be checked.

Contraception still matters

Tamoxifen is not a contraceptive and is unsafe in pregnancy. Non-hormonal methods such as a copper coil or condoms are usually advised.

When to report bleeding

Bleeding between periods, after sex, or bleeding after periods had stopped for a long time should be reported.

Some women stop tamoxifen early because they are frightened of womb cancer, often after hearing about it from friends or online.

Talk before stopping

Your oncologist can explain the balance of benefit and risk for you, and discuss alternatives if your concern is strong.

Clear plans reduce anxiety

Knowing exactly which symptoms to report, and whom to contact, helps many women feel more in control during treatment.