New evidence from two studies show that women who take tamoxifen to prevent or treat breast cancer are at greater risk of endometrial abnormalities, including cancer.
In the first, transvaginal ultrasound was used to monitor endometrial thickness in 247 tamoxifen users and 98 controls. In the drug group, endometrial thickness was almost three times that of non users. Rates of abnormal biopsies were also higher, especially if the women had symptoms of vaginal bleeding (J Clin Oncol, 2000; 18: 3464-70).
The second study involved 159 women who had endometrial biopsies annually for up to five years after beginning tamoxifen. Again, there were more abnormalities associated with bleeding (J Clin Oncol; 2000; 18: 3459-63).
Not all women on tamoxifen undergo strict regular surveillance of the endometrium. However, based on this new evidence, the authors conclude that yearly vaginal examinations are a rational consideration for women who don't want to end up trading one type of cancer for another.