Tamoxifen Side Effects 

For the most part, the side effects of tamoxifen (Nolvadex®) are alike to some of the symptoms of menopause. The most usual side effects are hot flashes and vaginal discharge. Some women experience irregular menstrual periods, headaches, tiredness, nausea and/or vomiting, vaginal dryness or itching, irritation of the skin around the vagina, and skin rash. As is the case with menopause, not all women who take tamoxifen will have these symptoms. Men who take tamoxifen may experience headaches, nausea and/or vomiting, skin rash, impotence, or a decrease in sexual interest.

Tamoxifen increases the chance of 2 types of cancer that can develop in the uterus: endometrial cancer, which arises in the lining of the uterus, and uterine sarcoma, which arises in the muscular wall of the uterus. Like all types of cancers, endometrial cancer and uterine sarcoma are potentially life-threatening. Women who have had a hysterectomy (surgery to remove the uterus) and are consuming tamoxifen are not at increased risk for these cancers.

(1)Endometrial cancer

In the BCPT, women who took tamoxifen had more than twice the chance of developing endometrial cancer compared with women who took a placebo (an inactive substance that looks the same as, and is administered in the same way as, tamoxifen). The risk of endometrial cancer in women taking tamoxifen was in the same range as (or less than) the risk in postmenopausal women taking single-agent estrogen replacement therapy. This risk is about two cases of endometrial cancer per 1000 women taking tamoxifen each year.

Most of the endometrial cancers that have occurred in women comsuming tamoxifen have been found in the early stages, and therapy has typically been effective. However, for some breast cancer patients who developed endometrial cancer while taking tamoxifen, the disease was life threatening.

(2)Uterine sarcoma

Information collected by the U.S. Food and Drug Administration indicates that women who have used tamoxifen for breast cancer treatment or prevention have an increased risk of developing uterine sarcoma. Review of all the NSABP clinical trials using tamoxifen confirmed an increased risk of this rare cancer. In the BCPT, there are about 2 cases per 10,000 women taking tamoxifen each year. Research to date indicates that uterine sarcomas are more likely to be diagnosed at later stages than endometrial cancers, and may therefore be harder to control and more life-threatening than endometrial cancer.

Abnormal vaginal bleeding and lower abdominal (pelvic) pain are symptoms of cancers of the uterus. Women who are consuming tamoxifen should converse with their physician about having regular pelvic examinations, and should be checked quickly if they have any abnormal vaginal bleeding or pelvic pain between scheduled exams. At this time, there is no evidence that tamoxifen is beneficial for women who do not have an increased risk of developing breast cancer.