Some breast cancer survivors have a higher-than-average risk of later developing another type of cancer, such as uterine cancer. Certain breast cancer treatments may raise the risk of second cancers. Tamoxifen is often prescribed to prevent breast cancer recurrence (when breast cancer comes back) in people who have treated hormone-positive breast cancer. Along with other risk factors, tamoxifen may affect your chances of developing uterine cancer.
Even if a breast cancer treatment may raise your risk of developing a second cancer, its benefits might outweigh this risk. It’s also important to understand that risk factors for cancer are complex. Continue reading to learn more about how tamoxifen treatment may affect your risk of uterine cancer and the signs and symptoms of uterine cancer.
Tamoxifen, sold under the brand name Soltamox, is a hormonal therapy used to prevent cancer from returning after treatment. Tamoxifen is also categorized as an adjuvant therapy, which means it’s used after treatments like surgery or chemotherapy to decrease the likelihood of cancer returning. Many people take tamoxifen for five to 10 years to treat or prevent certain types of breast cancer. It can decrease the risk of breast cancer recurring or new breast cancer developing by 30 percent to 50 percent.
Tamoxifen is in a class of medications called selective estrogen receptor modulators (SERMs). Tamoxifen is also known as an antiestrogen drug that works by blocking the effect of estrogen on hormone receptor-positive breast cancer. In this type of cancer, estrogen encourages breast cancer cells to grow and divide. By blocking the production of estrogen, tamoxifen can slow or stop cancer cell growth.
Your doctor may recommend tamoxifen if:
Tamoxifen can be taken whether or not you have gone through menopause.
The uterus is the largest component of the female reproductive system. This pear-shaped, hollow organ is located between the bladder and rectum in the pelvis (the area between the hip bones in the lower abdomen).
Uterine cancer — also called endometrial cancer or endometrial carcinoma — can develop when cells of the inner lining of the uterus begin to grow out of control. Uterine cancer is the most common gynecologic cancer, or cancer of the female reproductive system. In 2023, it’s estimated that more than 66,000 people in the United States will be diagnosed with uterine cancer, and more than 13,000 will die from the disease.
A tumor in the uterus can be benign (noncancerous) or cancerous. Examples of benign tumors include:
There are two main types of cancerous tumors in the uterus:
The exact cause of uterine cancer is unknown, but certain factors can increase your risk of endometrial cancer.
The use of tamoxifen is one factor associated with an increased risk of uterine cancer. If you’re taking (or have taken) tamoxifen, you have about a two to five times higher risk of developing uterine cancer. Although the odds may seem high with these numbers, the risk is still relatively low — about 1 in 500, according to the American Cancer Society.
Your risk of uterine cancer may increase the longer you take tamoxifen.
Tamoxifen use isn’t the only risk factor for uterine cancer. In fact, a history of breast cancer is also a risk factor for uterine cancer.
Additionally, breast cancer and uterine cancer share many of the same risk factors, including:
Your risk of developing uterine cancer can be influenced by many different factors, some of which you have control over and some you don’t. You may have more or fewer of these risk factors, including:
Talk to your doctor about your risk factors for uterine cancer.
Talk to your breast cancer health care team about which hormone therapy is best for you based on your risk factors. Treatment is a shared decision you should make together with your doctor to feel confident about your treatment plan. You can also talk to your doctor about potential risks and benefits of treatments to reduce the risk of tamoxifen-associated uterine cancer, such as:
If you’re worried about the effects of tamoxifen therapy on your risk for uterine cancer, you may wonder whether other breast cancer treatment options raise the risk as well.
Raloxifene (Evista) — another SERM used in breast cancer treatment — seems to have no effect on your risk of developing uterine cancer.
If you’ve already gone through menopause, you may be able to take an aromatase inhibitor — another type of hormone therapy that can decrease estrogen levels. Aromatase inhibitors have different side effects than tamoxifen and don’t cause uterine cancer. Taking aromatase inhibitors may result in fewer cases of uterine cancer compared to tamoxifen users. Examples of aromatase inhibitors include:
Regular testing for uterine cancer isn’t recommended unless you have symptoms or a high risk.
If you’re taking tamoxifen, you should be mindful of the signs and symptoms of uterine cancer. According to the American College of Obstetricians and Gynecologists (ACOG), postmenopausal women taking tamoxifen should be closely monitored for uterine cancer. Postmenopausal women should look for any vaginal bleeding during or after menopause. Pain in the pelvic area (the lower part of the abdomen between the hip bones) can also be a symptom of uterine cancer.
ACOG states that premenopausal women taking tamoxifen do not have an increased risk of uterine cancer. However, premenopausal women should still watch for the following symptoms:
If you experience symptoms of uterine cancer, you should talk to your doctor right away. They may order additional tests to help diagnose uterine cancer, such as:
If you have concerns about tamoxifen and your risk of developing uterine cancer, talk to your doctor. They can help you weigh the risks and benefits of taking tamoxifen as part of your breast cancer treatment.
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