Breast Cancer Drug Tamoxifen Does Not Increase Risk of Uterine Cancer

In lieu of the Breast Cancer Awareness Month, a new study reassured patients taking Tamoxifen that the breast cancer drug is safe and does not increase the risk of uterine cancer.

Despite being highly effective treatment and preventive measure for breast cancer, many women fail to take Tamoxifen due to fear of developing uterine cancer. Many health professionals believe that taking progestin along with Tamoxifen could decrease the risk of abnormalities in the endometrium or the inner lining of the uterus.

The study, published in the journal npj | Breast Cancer, showed no statistically significant difference in the risk of developing abnormalities in the inner lining of the uterus, which could lead to uterine cancer, between patients taking Tamoxifen alone and patients treated with Tamoxifen-progestin combination.

"Our study found that for women who did not have endometrial abnormalities when they began taking tamoxifen, there was a very low rate of developing pre-malignant conditions," said Ronald K. Potkul, MD, FACS, FACOG, chair of the department of obstetrics and oncology of Loyola University Chicago Stritch School of Medicine and first author of the study, in a press release.

For the study, the researchers enrolled 296 eligible postmenopausal breast patients with a type of early-stage breast cancer called estrogen receptor-positive. The participants were divided into two groups that either receives a Tamoxifen-only treatment or Tamoxifen-progestin treatment. Each participant underwent endometrial ultrasound at the beginning of the study and after two and five years.

After two years since the treatments began, 67 percent of women in the Tamoxifen-only group had a thickening of the inner lining of the uterus greater than 5 mm, while only 60 percent of the Tamoxifen-progestin group has thickened endometrium. These women underwent subsequent biopsies. Biopsy result showed that five cases of endometrial abnormalities in the Tamoxifen group, including four cases of proliferative endometrium (more cells than normal lining the uterus) and one case of simple hyperplasia (non-malignant clumping of cells). On the other hand, only one woman develop an endometrial abnormality on the Tamoxifen-progestin group.

The researchers noted that the difference between the Tamoxifen-only group and Tamoxifen-progestin group is not large enough to be considered statistically significant. Furthermore, the researchers believe that the lower endometrial abnormality rate in the study can be attributed to the screening requirements. With this, the researchers suggests that woman who are not sure about taking Tamoxifen should first undergo uterine ultrasound for additional reassurance.