A leiomyoma is a benign tumor that grows from smooth muscle cells. The most common type by far is the uterine leiomyoma, better known as a fibroid. By age 50, roughly 70% of white women and 80% of Black women will have developed at least one. While that prevalence is striking, many people never know they have fibroids because the growths often cause no symptoms at all.
Leiomyomas can also develop in other parts of the body where smooth muscle exists, including the esophagus, stomach, and skin. But uterine fibroids account for the vast majority of cases, so most of the medical attention (and most of what follows) centers on them.
How Leiomyomas Form and Grow
Each uterine fibroid starts as a single smooth muscle cell in the muscular wall of the uterus that begins dividing abnormally. This makes fibroids “monoclonal,” meaning every cell in a given fibroid traces back to one original cell. What triggers that first cell to go rogue isn’t fully understood, but hormones are the main fuel once growth begins.
Estrogen was long considered the primary driver, and it does play an important role. It triggers a chain of signals inside fibroid cells that promote cell division. But progesterone turns out to be equally significant. Studies show that when postmenopausal women take estrogen alone, fibroids show very little growth activity. Add progesterone to the mix, and the fibroids proliferate at rates similar to those seen in premenopausal women. This hormonal dependence is also why fibroids almost always shrink after menopause, when estrogen and progesterone levels drop sharply.
Types Based on Location
Fibroids are classified by where they sit relative to the uterine wall:
- Intramural fibroids grow within the muscular wall itself. They’re the most common type and can enlarge enough to distort either the inner cavity or the outer surface of the uterus.
- Submucosal fibroids develop just beneath the lining of the uterine cavity. Even small submucosal fibroids can cause heavy bleeding because of their proximity to the endometrium.
- Subserosal fibroids bulge outward from the uterus, with more than half their volume protruding beyond the outer surface. These are more likely to press on nearby organs like the bladder or rectum.
A single person can have fibroids in multiple locations simultaneously, and the specific mix of types largely determines which symptoms show up.
Common Symptoms
More than half of women with fibroids experience some combination of heavy menstrual bleeding, pelvic pain, or fertility problems. Heavy periods are the hallmark complaint, affecting up to 40% of those with fibroids. The bleeding tends to be worst with intramural fibroids, likely because these growths develop a surrounding layer of blood vessels that can rupture during menstruation.
As fibroids grow larger, they can create what doctors call “bulk symptoms.” The uterus becomes enlarged and irregularly shaped, pressing against surrounding structures. This can mean frequent urination (from bladder pressure), constipation (from rectal pressure), lower back pain, or a visible swelling of the lower abdomen. Some women describe feeling full or heavy in the pelvis even when they haven’t eaten.
Fibroids can also contribute to infertility, particularly submucosal ones that distort the uterine cavity and interfere with embryo implantation. That said, many women with fibroids conceive without difficulty.
How Leiomyomas Are Diagnosed
Most fibroids are first spotted on a transvaginal ultrasound, which is inexpensive, widely available, and requires no radiation. An ultrasound probe placed inside the vagina provides a close-up view of the uterus and can identify fibroids, measure their size, and give a rough sense of location.
When more detail is needed, MRI is the most sensitive imaging tool available. It’s better at counting the exact number of fibroids (especially small ones), pinpointing their precise location, and tracking changes in size over time. MRI is typically reserved for surgical planning or research settings because of its higher cost, but it provides consistently more accurate measurements than ultrasound.
Is Cancer a Concern?
One of the most common worries people have about fibroids is whether they can become cancerous. The short answer: it’s extremely rare. Leiomyosarcoma, the malignant counterpart, is found in roughly 0.1% to 0.3% of women who undergo surgery for presumed benign fibroids. One study of over 1,400 hysterectomies performed for benign fibroids found leiomyosarcoma in just seven cases (0.5%).
Whether fibroids actually transform into cancer or whether these rare cases were cancerous from the start remains debated. Either way, the risk is low enough that fibroids are not routinely biopsied or removed purely out of cancer concern. Rapid growth, unusual imaging features, or fibroids that appear after menopause may prompt closer evaluation.
Treatment Options
Many fibroids require no treatment at all. If they’re small, not growing, and not causing symptoms, monitoring with periodic ultrasounds is a perfectly reasonable approach.
Medications
Because fibroids depend on hormones to grow, most drug treatments work by dialing down estrogen and progesterone. Older injectable medications that suppress hormone production can shrink fibroids significantly but create menopausal side effects like hot flashes and bone density loss, which limits how long they can be used. Newer oral medications pair hormone suppression with low-dose “add-back” hormones to reduce bleeding while minimizing those side effects. Oral contraceptives and progestins can also help manage heavy bleeding, though they don’t shrink fibroids directly.
For bleeding specifically, a medication called tranexamic acid helps blood clot more effectively during periods and can reduce menstrual blood loss without affecting the fibroids themselves.
Procedures
When symptoms are severe or fibroids are large, procedural options include:
- Myomectomy: Surgical removal of fibroids while leaving the uterus intact. This is often preferred by women who want to preserve fertility. Recovery depends on whether it’s done through small incisions or a larger abdominal opening.
- Uterine artery embolization (UAE): A minimally invasive procedure where tiny particles are injected into the blood vessels feeding the fibroids, cutting off their blood supply. Most women experience a few days of cramping, low-grade fever, and fatigue afterward, but symptoms typically resolve within a week.
- Hysterectomy: Complete removal of the uterus. This is the only treatment that eliminates any possibility of fibroid recurrence, but it’s a permanent decision that ends the ability to carry a pregnancy.
A large clinical trial published in the New England Journal of Medicine compared myomectomy and UAE head to head. Complication rates were similar: 29% in the myomectomy group and 24% in the UAE group, a difference that wasn’t statistically significant. At two years, 93% of women who had myomectomy said they’d recommend the procedure to a friend, compared with 84% in the UAE group. Both approaches are considered effective, and the choice often comes down to fibroid size, location, and whether future pregnancy is desired.
Leiomyomas Outside the Uterus
Though far less common, leiomyomas can develop anywhere smooth muscle is found. The esophagus is the most notable non-uterine site. Esophageal leiomyomas are the most common benign tumors of the esophagus, though they’re still relatively rare in absolute numbers. They tend to cause no symptoms when smaller than 5 centimeters. Larger ones can cause difficulty swallowing, chest pain, heartburn, and occasionally regurgitation. Very large esophageal leiomyomas may appear as a mass in the chest on imaging and can cause a persistent cough.
Leiomyomas can also occur in the stomach, small intestine, bladder, and skin. In each location, they follow the same basic pattern: a slow-growing, benign mass of smooth muscle that only causes problems when it gets large enough to press on surrounding structures or disrupt normal function.