Tamoxifen & Uterine Cancer

Tamoxifen is a selective estrogen receptor modulator (SERM). It selectively inhibit the estrogen receptors in the breast but can selectively activate the estrogen receptors in the uterus. Tamoxifen therapy effectively reduces the risk of breast cancer recurrence.

In the National Surgical Adjuvant Breast and Bowel Project (Fisher 1994), the 5-year disease-free survival rate from breast cancer was 38% higher in the women taking tamoxifen. However, these women on Tamoxifen 20mg/day had a 1.6/1000 chance of developing endometrial cancer vs the background risk of 0.2/1000.

When the Project was extended to 10 years (Davis 2013), the risk of breast cancer recurrence and death was notably lower in women taking Tamoxifen.  The cumulative risk of endometrial cancer for women on long term Tamoxifen was 3.1% vs the background risk of 1.6%.

These results shows that the small risk of developing endometrial cancer is outweighed by the significant survival benefit of long term tamoxifen therapy.

Benefits of Tamoxifen Therapy
1. Reduced Breast Cancer Recurrence and Mortality
2. Reduced Osteoporosis
3. Improved Cholesterol Levels

Risks of Tamoxifen
1. Increased Uterine Cancer
2. Increased Blood Clots
3. Associated with Cataract

Side effects of Tamoxifen
1. Hot flushes, sweats and mood swings
2. Irregular vaginal bleeding
3. Vaginal dryness, itch and discomfort
4. Nausea, loss of appetite and vomiting
5. Fluid retention

American College of OBGYN Committee Opinion  on Tamoxifen Treatment
1. Tamoxifen use may be extended to 10 years.
2. Women on Tamoxifen should be advised of the small risk of uterine cancer.
3. In asymptomatic women using tamoxifen, screening for endometrial cancer with routine transvaginal ultrasound and/or endometrial biopsy has not been shown to be effective.
4. Any abnormal vaginal bleeding, bloody vaginal discharge, staining, or spotting should be investigated.
5. There may be a role for pretreatment screening of postmenopausal women before starting tamoxifen therapy.