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Breast Cancer, Uterine Cancer and Tamoxifen


K, 56, was taken aback when she noticed brown vaginal discharge on her underwear. She knew she had to have a gynaecological consultation immediately, as advised by her oncologist. She had breast cancer 2 years ago and had a mastectomy done. The tumor was hormone sensitive and she was given tamoxifen soon after the surgery.


Gynaecological examination did not reveal any pelvic masses. The uterus and cervix appeared normal. Stale blood was seen at the cervical opening. Ultrasound examination showed that the uterine lining (endometrium) appeared thickened and measured 14mm.


What is tamoxifen?

Tamoxifen belongs to a group of medications called selective oestrogen receptor modulator (SERM). It can act like oestrogen on some tissues and block the effects of oestrogen on other tissues in the body. It is thus known as a Janus-headed drug.


What is tamoxifen used for?

Tamoxifen was originally developed as a contraceptive morning-after pill but was found to be ineffective. However, its anti-oestrogenic properties were soon discovered to be effective in the treatment of hormone dependent breast cancer. Because of the low toxicity and wide availability, it has become one of the most frequently prescribed anticancer drugs worldwide in the last decades.


The drug has been approved by the U.S. Food and Drug Administration for the following indications:

  • In women at high risk of breast cancer, it helps lower the risk of developing breast cancer.

  • For women with breast cancer treated with surgery, it can help lower the chances of the cancer recurring and improve the chances of survival. It can also lower the risk of a new cancer developing in the other breast.

  • For women with breast cancer that has spread to other parts of the body,

What is the relationship between Tamoxifen and uterine cancer?

While Tamoxifen is efficacious in the treatment of breast cancer, it can increase the risk of uterine cancer (endometrial cancer) especially in postmenopausal women with preexisting pathologies in the uterus. Most studies have found that the increased risk is about two to three times higher than that of the general population. Besides endometrial cancer, tamoxifen can cause a group of cancers of the uterine muscle (sarcoma). But these cancers are very rare.


Paradoxically, tamoxifen can also be used to treat certain forms of advanced endometrial cancer. This is another indication of this Janus-headed drug.


The molecular mechanisms for the Janus-headed activity of tamoxifen remain elusive.


What are the things to look out for while taking tamoxifen?

It is recommended that any abnormal vaginal bleeding, bloody vaginal discharge, staining, or spotting while the patient is under the medication should be investigated straightaway. This is to rule out endometrial cancer as well as other non-cancerous uterine lesions that the drug may cause.


K underwent a hysteroscopy and endometrial curetting. Pathology report revealed uterine polyps with no cancer detected. She was very relieved with the result and continued with tamoxifen therapy.

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