• Dr Peter Chew

Breast cancer and the womb

You should have your womb checked as you have been taking tamoxifen for a while now,"  the oncologist advised M, a 52-year-old housewife who had a stage I cancer in her right breast 2 years ago.


The cancer was detected during a mammographic examination at her annual health screen. It was small, about 5 mm  in size. The lymph nodes in the axilla were not involved. M decided to have a lumpectomy, in which the tumour, together with part of the right breast, was excised. After the surgery, she had radiotherapy, followed by hormone therapy since the cancer cells were positive for oestrogen receptor.


Breast cancer is the most common cancer among Singaporean women accounting for more than 25% of all female cancers. According to statistics, between 2011 and 2015, there were 1,927 women diagnosed with breast cancer and over 400 deaths from the disease each year. These figures will escalate with our ageing population as the risk of getting breast cancer increase with age. Chinese women are at a higher risk, when compared with Malays and Indians.


Depending on whether the cancer has spread within the breast or to other parts of the body, breast cancer is classified into 5 stages. The stages are the numbered zero (in situ carcinoma, which means it is not invasive and does not have metastatic potential) and the Roman numerals I, II, III, or IV. The higher the number, the more advanced the cancer. In M’s case, her cancer was stage I, indicating that the growth is less than 2 cm without spreading to the axillary lymph nodes.


Treatment for breast cancer consists of surgery, radiotherapy as well as drug treatments like chemotherapy, hormonal (also known as endocrine) therapy and targeted therapy that are used after surgery to lower the risk of relapses and improve the cure rate. About 80% of all breast cancers are “oestrogen receptor-positive.” (ER+) which means the cancer cells will grow in response to the female hormone oestrogen. In M’s case, tamoxifen was used to suppress the influence of oestrogen on the cancer cells.


Tamoxifen is a non-steroidal anti-oestrogen. It is the most commonly prescribed drug and can be given for 5 years or more. However, it has a drawback. Although effective in suppressing breast cancer cells, it can stimulate the cells lining the cavity of the womb (endometrium). As a result, the endometrial cells may become hyperactive (endometrial hyperplasia), uterine polyps may occur and uterine cancer may develop. 


Nevertheless, studies have shown that the small risk of developing uterine cancer is outweighed by the significant survival benefit. The committee of gynaecologic practice of the American college of Obstetricians and Gynaecologists in 2014 stated that tamoxifen use may be extended to 10 years based on data demonstrating additional benefit. But patients should be warned about the risks of abnormal changes in the lining of the womb and womb cancer.

M did not have any abnormal vaginal bleeding, bloody vaginal discharge, staining, or spotting. The thickness of her endometrium was less than 5 mm on ultrasound examination, which indicated that there was no obvious abnormal cellular activity. She understood the possible side effects of tamoxifen on her womb and agreed to come for monitoring on a yearly basis.

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