Because the drug tamoxifen can increase the risk for endometrial cancer (cancer of lining of the uterus), many women who take tamoxifen to treat or prevent breast cancer undergo routine ultrasound screenings and biopsies to help detect endometrial cancer. However, two recent studies reveal that transvaginal ultrasound and uterine biopsies do not benefit women on tamoxifen. According to researchers from both studies, vaginal bleeding is an early warning sign of endometrial cancer, and is more effective at signaling cancer than uterine screening or biopsy.

In the first of two studies on tamoxifen and endometrial cancer published in the October 15, 2000 issue of the Journal of Clinical Oncology, researchers performed endometrial biopsies every six months for five years on 111 breast cancer patients who were taking tamoxifen. Of these women, nearly 13% underwent invasive uterine procedures (called D & C for dilation and curettage) after their biopsies revealed abnormalities. None of the women were found to have endometrial cancer.

According to Richard Barakat, MD and his colleagues from the Sloan-Kettering Cancer Center in New York, the results of the study should prevent the hundreds of thousands of women on tamoxifen and the 80,000 women who will begin taking tamoxifen each year from undergoing unnecessary invasive uterine procedures that rarely detect cancer. Performing a uterine biopsy after a woman reports vaginal bleeding is as effective at detecting cancer as performing a routine uterine biopsy for screening purposes and is significantly less traumatic for the patient, said Dr. Barakat.

In another study published in the Journal of Clinical Oncology, researchers also found that routine uterine screenings, which have been suggested to be necessary for women on tamoxifen, were ineffective at detecting endometrial cancer. According to Bernd Gerber, MD and his colleagues from the University of Rostock in Rostock, Germany, tamoxifen can cause the endometrium (lining of the uterus) to thicken and swell, which can resemble cancer on a transvaginal ultrasound monitor.

In the study, 247 women on tamoxifen and 98 healthy women underwent transvaginal ultrasound exams every six months for five years. 52 of the patients were referred for uterine biopsies based on the results of their ultrasound exams even though the women did not report vaginal bleeding (a warning sign for endometrial cancer). Only one of the 52 women who underwent biopsy was diagnosed with endometrial cancer. However, in the study, 20 women on tamoxifen reported vaginal bleeding. After performing biopsies on these 20 women, 2 of the women were found to have endometrial cancer.

According to Dr. Bernd and his colleagues, transvaginal ultrasound has a high false positive rate (indicates cancer when cancer is not present) and consequently, many women are referred for unnecessary and often painful invasive procedures. Because the cervix of a post-menopausal woman is closed, a uterine biopsy requires dilation and curettage (removing uterine cells by scraping them with an instrument called a curette). D & C is an invasive procedure that often requires general anesthesia.

Researchers from both studies say that vaginal bleeding is a better indicator of endometrial cancer than both biopsy and ultrasound screening. Women on tamoxifen should immediately report vaginal bleeding to their physicians. However, in approximately 85% of cases, vaginal bleeding is the sign of a benign (non-cancerous) and treatable condition. In 15% of cases, vaginal bleeding can indicate a serious condition.

According to large studies conducted by the National Surgical Adjuvant Breast and Bowel Project (NSABP) and other researchers, women who take tamoxifen are approximately 2.5 times more likely to develop endometrial cancer than women who are not taking tamoxifen. However, the risk of endometrial cancer is still low for women on tamoxifen. Approximately 2 of every 1000 women on tamoxifen will develop endometrial cancer. For this reason, the benefit of treating or preventing breast cancer with tamoxifen often outweighs the risk of developing endometrial cancer for many women.

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