Uterine fibroids and cancer: Is there a connection?

Uterine fibroids are smooth-muscle tumors that develop in the thick muscular walls of the uterus. We don’t know for certain what causes them, but they happen when individual smooth-muscle cells start growing out of control.

But are uterine fibroids the same thing as endometrial cancer? What are their symptoms, and how are they diagnosed?

Read on for answers to these and four more questions I often hear about uterine fibroids. 

Are uterine fibroids cancerous?

Uterine fibroids, also known as leiomyoma, are always benign tumors. That means they are never cancerous.

Though there have been a few case reports that show a transition of a benign leiomyoma into a cancerous leiomyosarcoma, researchers argue that the malignant transformation is unproven.

Endometrial cancer is a glandular disease that starts in the lining of the uterus. Leiomyomas stem from a completely different cell type. 

Leiomyomas are also extremely common, especially among Black women. About 60% of white women and 70% of Black women will have uterine fibroids by age 52.

Do uterine fibroids have any symptoms?

The most common symptoms of uterine fibroids are:

• pelvic pain and pressure
• heavy vaginal bleeding during periods 

Fibroids can be so small that some women don’t even know they have them. 

When uterine fibroids do cause symptoms, they tend to be mild and develop gradually. You might feel an uncomfortable pressure in your pelvis sometimes, for instance, rather than a sudden severe pain in your abdomen. You also might notice that your lower abdomen appears slightly distended or feels bloated.

Fibroids can interfere with fertility, too, so trouble conceiving might be a symptom.

How are uterine fibroids diagnosed?

Normally, it’s when a regular pelvic exam reveals a pelvic mass, and your gynecologist orders an ultrasound to see what’s going on. Other times, uterine fibroids are found incidentally on pelvic imaging.

But not all things that look like leiomyomas are necessarily leiomyomas. 

A type of soft tissue sarcoma called leiomyosarcoma is another possibility. These are very, very rare, though. The incidence of leiomyosarcoma is only about 1 in 100,000 people per year, but leiomyosarcoma is the second-most-common type of uterine malignancy behind endometrial cancer.

The only way to definitively diagnose it is through pathology, but less than 1% of the uterine tumors we see here at MD Anderson are leiomyosarcomas.

One thing to note is that leiomyosarcoma symptoms are very different from fibroid symptoms and endometrial cancer symptoms. Leiomyosarcomas can double in size in just a month. So, if you’ve got a rapidly enlarging mass in your pelvis, it’s probably not a fibroid.

Can fibroids develop anywhere other than the uterus?

Sometimes, they develop in other parts of the pelvis, such as the cervix or the ovaries. But they are found most frequently in the walls of the uterus.  

Do uterine fibroids increase your risk of endometrial cancer?

No. Uterine fibroids are not associated with an increased risk for any type of cancer.

How are uterine fibroids normally treated?

If you’re only having marginal or mild symptoms, we usually leave them alone and practice what we call “watchful waiting.” The same applies if your fibroids are found incidentally, and they’re not causing you any pain or excess bleeding.

If it’s your very first pelvic exam, though, and we discover a fibroid larger than 5 cm (about 2 inches) across, we’ll repeat the ultrasound in five or six months to make sure it’s not growing rapidly. If it is, we might take it out, depending on its size and your symptoms. If it’s not growing, we’ll keep monitoring it, and if you develop symptoms over time, we’ll start with non-surgical interventions.

Non-surgical interventions for leiomyoma include:

• NSAIDs, such as ibuprofen, to reduce bleeding
• Oral contraceptives to keep your hormones steady, since sharp fluctuations can make them grow

If these don’t work to reduce the symptoms, we’ll consider one of the following types of surgery for leiomyoma:

• Myomectomy, or removal of the fibroids to preserve fertility
• Embolization, a procedure that cuts off the fibroids’ blood supply, shrinking them
• Hysterectomy, or removal of the entire uterus

Hysterectomy used to be the main surgery used for fibroid uteruses, but now we strive to use the least-invasive methods first. We’ll only do a hysterectomy if none of the other options work.

What’s the one thing you want people to know about uterine fibroids?

Uterine fibroids tend to be very estrogen- and progesterone-sensitive, so they grow in response to these hormones. But estrogen and progesterone levels drop sharply after menopause, so if you have fibroids, they’ll usually shrink at that point.

Elizabeth Keeler, M.D., is a gynecologist who specializes in the care of women with cancer. 

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