Are Fibroids Cancerous?

Fibroids rarely develop into cancer

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Fibroids are benign (noncancerous) tumors made of smooth muscle. They most often grow in a person’s uterus during their childbearing years. There are several types of fibroids, including:

  • Submucosal: Grow inside the uterine cavity
  • Intramural: Embed into the muscle wall of the uterus
  • Subserosal: Grow along the outside wall of the uterus
  • Pedunculated: Connected to the outside of the uterus by a thin stem

Fibroids can range in size from 1 millimeter to 8 inches or larger. Some grow as large as a small melon.

The exact cause of fibroids is unknown. However, certain risk factors—such as being Black, having a family history of fibroids, and obesity—may make you more prone to developing them.

It's important to know that fibroids are usually not cancerous. However, in rare cases, they can develop into cancer. 

Person with brown skin places their hands over their lower abdomen

Grace Cary / Getty Images

Cancerous Fibroids

Fewer than 1 in 1,000 fibroids will develop into cancer. Cancerous fibroids are a form of leiomyosarcoma, a cancer of the smooth muscles.

These cancers are not believed to develop from an existing fibroid, nor does having fibroids increase your risk of developing cancer.

The Research

According to the Food and Drug Administration (FDA), uterine sarcoma is more common in people undergoing surgery for uterine fibroids than was previously thought.

Since it can be hard to distinguish between fibroids and sarcoma before surgery, the FDA says that surgery with laparoscopic power morcellators—which cut tissue into smaller pieces to be removed through a small incision site—may increase the risk of spreading cancerous tissue.

By the FDA’s estimate, as many as 1 in 580 to 1 in 225 people undergoing surgery for fibroids may have hidden sarcoma. In addition, the FDA estimates that 1 in 1,100 to 1 in 495 people undergoing surgery for fibroids may have leiomyosarcoma.

However, not all researchers agree with the FDA’s estimates. For example, the Agency for Healthcare Research and Quality (AHRQ) conducted a systematic review that found a much lower incidence of leiomyosarcoma.

The AHRQ's review of 160 studies, which included 10,000 people, found that those undergoing surgery for fibroids have leiomyosarcoma at a rate of 0 to 13 out of 10,000.

The American College of Obstetricians and Gynecologists (ACOG) recommends informing patients of the risk of unexpected leiomyosarcoma as being between 1 in 495 (the FDA’s estimate) and less than 1 in 10,000 (AHRQ’s estimate). ACOG recommends using imaging, cervical cancer screening, and endometrial tissue sampling to rule out malignancy before surgical morcellation to reduce risk.

Risk Factors

Uterine sarcomas are rare. Leiomyosarcomas occur at a rate of approximately 0.4 to 0.64 per 100,000 people.

While developing a cancerous fibroid is unlikely, researchers have identified certain risk factors that may place people at greater risk.

You might be more likely to develop a cancerous fibroid if you:

  • Are older
  • Are postmenopausal
  • Have a history of cancer in other parts of the body
  • Have subserosal fibroids
  • Have a solitary fibroid
  • Have a documented history of rapid fibroid growth

Selecting the Right Treatment

Not everyone requires fibroid treatment. If your fibroids do not cause symptoms, your doctor may suggest a watch-and-wait approach.

If your fibroids cause discomfort, however, fibroid treatment may include medication or surgery. As mentioned, a common surgical technique, morcellation, can spread undetected uterine sarcoma. 

Morcellation is used during a myomectomy, a surgical procedure that removes fibroids without removing the uterus. Morcellation uses laparoscopic power morcellators to cut tissue into smaller pieces to be removed through a small incision site.

Since the FDA outlined the risk the device carries of spreading cancer and lowering a person’s chance of long-term survival, people have been wary of the procedure to treat fibroids. 

While ACOG recommends cancer screening prior to morcellation, they also acknowledge that leiomyosarcoma is not reliably detected before surgery. Most leiomyosarcomas are discovered during surgery.

If cancer is suspected, hysterectomy is the first-line treatment. Hysterectomy involves the surgical removal of the uterus. Sometimes other reproductive organs, like the cervix, ovaries, fallopian tubes, and part of the vagina, are also removed during the procedure. Your surgeon will also likely remove lymph nodes to determine whether the malignancy has spread.

Further treatment depends on the stage of cancer. Chemotherapy, radiation, targeted drugs, and hormone therapy might also be used.

Frequently Asked Questions

How do I know if my fibroids are cancerous?

Most of the time, fibroids are benign. However, they can be cancerous in rare cases. If your doctor thinks you may have cancer, they might recommend that you have an ultrasound to give them a better look at the growth. They might also want to do an endometrial biopsy to see if there are cancer cells present in the lining of your uterus.

Less than half of leiomyosarcomas are found through an endometrial biopsy because this type of cancer starts in the muscle wall and wouldn't be detected in the uterine lining until it spreads there.

The only way to definitively diagnose leiomyosarcoma is to remove it with surgery.

How often are fibroids cancerous?

Fibroids are most common in people who are in their 40s and 50s. Up to 80% of people will have had fibroids by the time they reach 50 years old. Fibroids are almost always benign—fewer than 1 in 1,000 will develop into cancer.

What types of fibroids are more likely to be cancerous?

Subserosal fibroids—those that grow along the outside wall of the uterus—are more likely to be cancerous than other forms of uterine fibroids. In addition, single fibroids are more likely to be cancerous than are multiple fibroids.

A Word From Verywell

If you have recently been diagnosed with uterine fibroids, you might be worried about whether they could be cancerous. Rest assured that 999 times out of 1,000, fibroids are benign.

However, if fibroids are causing you pain and other symptoms, it's important to talk to your doctor about your treatment options.

There is conflicting research about morcellation's risk of spreading undetected cancer; while morcellation is less invasive than some other treatments, it is not the only treatment option.

For some people—specifically, younger people who wish to maintain their fertility—the benefits of morcellation may outweigh the risks. For others—such as those who have known or suspected cancer—morcellation would not be an option.

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