Can uterine fibroids be cancerous?

Although uterine fibroids are usually benign, in very rare circumstances uterine fibroids can be cancerous. Cancerous fibroids, called leiomyosarcomas, occur in less than 1 in 1,000 fibroid cases, and doctors think that they develop on their own rather than from existing fibroids that are benign.

Having benign uterine fibroids is not associated with an increased risk of developing other types of uterine cancers, nor does having benign fibroids increase your odds of developing a cancerous fibroid in the future.

Although leiomyosarcomas are rare and can occur almost anywhere in the body, they most commonly arise in the uterus or abdomen. Originating from your body’s smooth muscle cells, leiomyosarcomas are categorized as soft tissue sarcomas, malignancies of the connective tissue supporting your body’s organs and other structures. Though the cause of leiomyosarcomas is not known, they make up about 10 to 20 out of every 100 soft tissue sarcomas. Statistically, uterine leiomyosarcomas affect 6 out of 1 million people annually in the United States.

Leiomyosarcoma symptoms

Similar to benign fibroids, leiomyosarcomas may not cause any symptoms in their early stages, but as they grow larger, abdominal swelling may occur; these tumors are usually aggressive, meaning that they grow and spread quickly. As the cancerous cells of a leiomyosarcoma tumor multiply and the tumor becomes larger, you may be able to feel a mass when you touch your pelvic area.

Larger cancerous uterine fibroids often begin to cause:

• Abnormal bleeding
• Abnormal vaginal discharge
• Changes in urination and bowel movements

Other symptoms are more general and are common with many types of cancer, such as:

• Fatigue
• Fever
• Unexplained weight loss
• Feeling unwell overall
• Nausea
• Vomiting

Usually, your doctor will order imaging tests such as an MRI, CT scan, PET scan or angiography if you’re experiencing symptoms of leiomyosarcoma. These images will be used to help determine the location and size of the tumor and to see if there are any signs that it has spread, which may indicate the presence of cancerous cells. A biopsy is the only way to know for sure if a uterine fibroid is cancerous, so a tissue sample may be taken and analyzed in a laboratory to determine whether the fibroid is in fact a leiomyosarcoma.

Leiomyosarcoma treatment

If your biopsy confirms that you have a leiomyosarcoma, there are several possible treatment options. Your treatment will depend on how big your tumor is, where it is and whether it has spread.

Tumors that can be completely removed have a higher probability of being cured; if cancerous tissue or cells remain in the body, the tumor is more likely to grow back in the same spot or elsewhere. If the tumor cannot be fully removed via surgery, radiation therapy may be used to target the area in order to prevent any leftover cancerous cells from multiplying. If a leiomyosarcoma is very big or it has spread to other areas of your body, surgery and chemotherapy may both be recommended.

Although it’s common for women to develop uterine fibroids, it is highly unlikely that they will be cancerous. Leiomyosarcomas of the uterus are extremely rare.