Can a fast-growing fibroid be cancer?

Fibroids don't "turn into" cancer; what leiomyosarcoma is

Uterine fibroids (leiomyomas) are benign growths of the muscle wall of the uterus, and they are not thought to turn into cancer over time. A different, separate tumor, leiomyosarcoma, is a rare cancer that starts in the same muscle layer and can look like a fibroid on imaging; it is usually found only after tissue is removed and examined under a microscope. In a population-based study of hysterectomies done for presumed benign reasons, an unexpected sarcoma was found afterward in about 1 in 752 hysterectomies overall, and specifically in about 1 in 256 (0.39%) of the hysterectomies done for presumed fibroids².

What counts as "fast growth", and why it's an unreliable sign

"Fast-growing fibroid" is not a single defined test, and different studies have used different cutoffs for rapid growth, so this page does not quote one definition that fits every report. What the evidence does show is that growth rate alone is a poor way to predict sarcoma. In one study of this question, 1,332 women had surgery for a presumed fibroid; sarcoma was found in 0.23% overall, versus 0.27% of the 371 women operated on specifically because of rapid growth, and in none of the 198 women who met a stricter published definition of rapid growth¹. The study's authors concluded that rapid growth did not substantiate an increased risk of sarcoma.

Growth after menopause

Fibroids tend to shrink after menopause⁷, and age and menopausal status also change how new growth is interpreted. In a single-center study of 1,398 women having surgery for presumed fibroids, the chance of an unexpected leiomyosarcoma rose from 0 of 561 (0%) in women under 40, to 1 of 673 (0.15%) at ages 40–49, to 2 cases (1.2%, about 1 in 82) in women over 49, based on 3 cases in total³. A separate population-based study found unexpected sarcoma in a small number of cases, more often among peri/postmenopausal women than premenopausal women having fibroid surgery (1 of 174, or 0.57%, vs 3 of 851, or 0.35%), and identified being peri/postmenopausal, having a large uterus, and being 45 or older as risk factors for sarcoma². If you notice a new or growing fibroid-like mass after menopause, it is worth raising with your clinician.

What ultrasound and MRI can and can't tell you

Ultrasound is the first-line imaging test for suspected fibroids⁸. When there's concern about distinguishing a benign fibroid from a leiomyosarcoma, MRI is the modality most of the research on this question has focused on. A 2023 expert consensus statement reviews using MRI to evaluate uterine masses for leiomyosarcoma risk, noting that research since 2014 suggests leiomyosarcoma may be found in as high as 1 in 770 (0.13%) of all resected masses that were presumed, before pathology, to be a fibroid⁶. That is a broader surgical population than the hysterectomy-specific 1-in-256 estimate above, which is part of why the two figures differ. On MRI, specific qualitative features, nodular borders, internal hemorrhage, dark areas on T2-weighted images, and unenhanced regions, are strongly associated with leiomyosarcoma rather than an atypical (unusual-looking) fibroid; in a small study of 41 women, a lesion with 3 or more of these 4 features was identified as leiomyosarcoma with high sensitivity and specificity⁵. Even so, no single feature or test is certain on its own, which is part of why unusual, worsening, or postmenopausal findings are discussed with your care team rather than read as reassuring alone.

If your report uses unfamiliar terms, the fibroid MRI report guide can help turn them into questions, and it also covers ultrasound language.

Why this matters for choosing a treatment

Because leiomyosarcoma cannot be reliably diagnosed before surgery, professional guidance calls for shared decision-making, including informed consent about the risks and benefits of each surgical approach, whenever a presumed fibroid is being removed⁴. That matters most for morcellation, cutting the uterus or a fibroid into smaller pieces so it can be removed through a small incision, because morcellating an undiagnosed sarcoma can spread cancer cells in the pelvis⁴. Since 2014, that risk has led to tighter regulation of laparoscopic power morcellation^2,6. Uterine fibroid embolization (UFE) works differently: it blocks blood flow to fibroids rather than removing and examining tissue, so it does not give your care team a pathology specimen the way surgery can. In a study of 346 women followed after UFE or focused-ultrasound treatment for presumed fibroids, 4 (1.2%) were later diagnosed with leiomyosarcoma, a higher rate than earlier reports. The authors recommend a thorough workup and counseling before treatment⁹. Ask your doctor how that was weighed in your case. For a broader look at the options, see non-surgical fibroid treatment, and if hysterectomy is part of the conversation, questions to ask before hysterectomy.

Warning signs: call now

Call your clinician promptly (not necessarily the emergency room) if you notice a pelvic mass or fibroid-like growth that is new or enlarging after menopause, rapid growth together with new pain or bleeding, or an imaging report that mentions features such as nodular borders, internal hemorrhage, or unusual enhancement.

Go to urgent or emergency care for heavy or uncontrolled vaginal bleeding, fainting, sudden severe pelvic or abdominal pain, fever with pelvic pain, or any pregnancy-related bleeding or pain.

Talk with your doctor before you decide. This information does not replace personal medical advice. Read the medical disclaimer.

Sources

1. Parker et al., uterine sarcoma in patients operated on for presumed or rapidly growing leiomyoma, Obstet Gynecol 1994, PMID 8127535 ↩︎
2. Multinu et al., population-based incidence of sarcoma at hysterectomy for benign indications, Am J Obstet Gynecol 2019, PMID 30447212 ↩︎
3. Rey Valzacchi et al., incidence of leiomyosarcoma at surgery for presumed myomas by age group, J Minim Invasive Gynecol 2020, PMID 31260748 ↩︎
4. ACOG Committee Opinion No. 822, Uterine Morcellation for Presumed Leiomyomas, Obstet Gynecol 2021, PMID 33595252 ↩︎
5. Lakhman et al., MRI differentiation of uterine leiomyosarcoma from atypical leiomyoma, Eur Radiol 2017, PMID 27921159 ↩︎
6. Hindman et al., MRI evaluation of uterine masses for risk of leiomyosarcoma: a consensus statement, Radiology 2023, PMID 36194109 ↩︎
7. Lethaby and Vollenhoven, fibroids (uterine myomatosis, leiomyomas), BMJ Clin Evid 2015, PMID 26032466 ↩︎
8. Woźniak and Woźniak, ultrasonography of uterine leiomyomas, Prz Menopauzalny 2017, PMID 29483851 ↩︎
9. Leonardo-Pinto et al., diagnosis of gynecologic malignancy after interventional radiology treatment of presumed fibroid disease, Fertil Steril 2023, PMID 36871858 ↩︎