Key Facts
- Fibroids themselves are benign and do not turn into cancer. The rare uterine cancer sometimes confused with fibroids, leiomyosarcoma, is a genetically distinct tumor that does not arise from a preexisting fibroid.
- Based on the largest available analysis (AHRQ, 2017; 136,195 women), the risk of finding an unexpected leiomyosarcoma during surgery for presumed fibroids ranges from about 1 in 770 to fewer than 1 in 10,000.
- Rapid fibroid growth alone is not a reliable sign of cancer. A landmark study found sarcoma in 0.27% of women operated on for “rapidly growing” fibroids, essentially the same as the baseline rate.
- New or enlarging uterine growth after menopause is different and deserves prompt evaluation, since fibroids are estrogen-driven and typically shrink or stabilize once estrogen declines.
- Dr. Kim has personally published peer-reviewed research on using MRI and blood testing to screen for risk before fibroid surgery.
- When any uncertainty exists, Dr. Kim uses contained morcellation, a technique that seals tissue in a specialized bag before removal so nothing can spread if an unsuspected malignancy were present.
If you were just told you have fibroids and now you are searching whether they can turn into cancer, that is a reasonable question to want answered directly. Here it is: fibroids do not become cancerous. The rare cancer sometimes mistaken for a fibroid before surgery, leiomyosarcoma, is a separate disease, and the odds of encountering it are low.
What Is the Difference Between a Fibroid and Uterine Cancer?
A uterine fibroid, also called a leiomyoma, is a benign smooth-muscle growth in the uterine wall. Fibroids are extremely common, affecting up to 80% of women by age 50, and the overwhelming majority never cause a problem beyond symptoms like heavy bleeding or pelvic pressure.
Leiomyosarcoma is a malignant tumor that also arises from uterine smooth muscle, which is why it can occasionally resemble a fibroid on imaging before pathology confirms which one you have (GCIG Consensus Review). The important distinction: leiomyosarcoma is genetically distinct from the start. It does not develop from a fibroid that was already there.
How Common Is It for a “Fibroid” to Actually Be Cancer?
The 2017 Agency for Healthcare Research and Quality (AHRQ) report, the largest and most rigorous analysis available, reviewed 160 studies covering 136,195 women having surgery for presumed fibroids. It found the risk of discovering an unexpected leiomyosarcoma ranged from about 1 in 770 to fewer than 1 in 10,000 surgeries (ACOG Committee Opinion No. 770). That figure describes women already having surgery for symptomatic fibroids, itself a small subset of all women with fibroids, so the risk across all women with fibroids is smaller still.
Does Rapid Fibroid Growth Mean Cancer?
This is one of the most persistent myths in fibroid care, and it drives a lot of unnecessary fear.
A widely cited study reviewed 1,332 women who had surgery for presumed fibroids, including 371 women specifically operated on because their fibroids were “rapidly growing.” The incidence of sarcoma in that rapid-growth group was 0.27%, statistically no different from the 0.23% rate across the full study population (Parker, Berek, and Fu, Obstetrics and Gynecology, 1994). Growth speed on its own did not predict cancer.
One exception matters. Fibroids are estrogen-driven, so they typically stabilize or shrink after menopause. A new or growing uterine mass discovered after menopause is a different clinical picture than rapid growth during the reproductive years, and it warrants prompt evaluation.
What Are the Real Risk Factors for Uterine Sarcoma?
Most women who develop leiomyosarcoma have no identifiable risk factor. The established ones, per the American Cancer Society, include:
- Age. Risk increases with age, and most cases are diagnosed in women 50 and older.
- New growth after menopause. As mentioned above, this is a more meaningful signal than growth speed alone.
- Prior pelvic radiation, typically for cervical or rectal cancer, with sarcomas appearing 5 to 25 years later.
- Long-term tamoxifen use, usually for breast cancer treatment, with sarcomas typically appearing 2 to 5 years after starting.
- Hereditary leiomyomatosis and renal cell cancer (HLRCC), a rare inherited condition.
- Race. Leiomyosarcoma is diagnosed more often in Black women than in White women, for reasons that are not fully understood.
Symptoms of leiomyosarcoma, when present, look like ordinary fibroid symptoms: bleeding, pelvic pain, pressure. This overlap is exactly why imaging and clinical judgment matter more than symptoms alone.
How Is a Fibroid Evaluated for Safety Before Treatment?
Because leiomyosarcoma cannot be reliably diagnosed before surgery on symptoms alone, evaluation relies on imaging, and sometimes blood testing, to flag higher-risk cases.
Dr. Kim co-authored a peer-reviewed study on exactly this question: her institution required preoperative MRI with diffusion-weighted imaging plus a lactate dehydrogenase (LDH) blood test before fibroid surgery, then tracked the effect on surgical decisions across 1,085 women (Kim et al., PLoS One, 2021). Abnormal MRI findings meant a far higher chance of being directed to open surgery over a minimally invasive approach (65% vs. 35%), rising further when LDH was also abnormal (70% vs. 17%). The overall rate of malignant diagnoses did not change significantly after the protocol began. What changed was the surgical decision-making, directing higher-risk cases toward the more cautious approach, which is the point of preoperative screening.
How Kim Gyn Manages This Risk During Fibroid Surgery
When a fibroid comes out through a small incision, the tissue sometimes needs to be divided into smaller pieces, a technique called morcellation. In 2014, the FDA warned against uncontained power morcellation because of the risk that an unsuspected malignancy could spread within the abdomen. The FDA did not prohibit morcellation altogether; it has since recommended contained morcellation specifically, in which the tissue is sealed inside a specialized bag before it is divided, so nothing spills and nothing contacts the surrounding tissue.
Dr. Kim uses contained morcellation as standard practice, and all removed tissue is sent for pathologic analysis regardless of preoperative imaging results.
Having multiple fibroids, or large ones, does not itself signal higher cancer risk. In one recent case, Dr. Kim performed a robotic myomectomy removing 11 fibroids weighing over 1,000 grams total, entirely benign. Fibroid number and size are surgical planning factors, not red flags for malignancy on their own.
Key takeaway: fibroids are common, benign, and do not become cancerous. The rare cancer sometimes confused with fibroids is a separate disease with a low but real incidence, which is exactly why preoperative imaging, careful surgical planning, and pathologic review of all removed tissue matter, not because fibroids themselves are dangerous.
Frequently Asked Questions About Fibroids and Cancer
Can a fibroid turn into cancer?
No. As explained above, leiomyosarcoma is genetically distinct from the start, not a fibroid that has transformed. The two happen to arise in the same tissue type, which is why they are sometimes confused before pathology confirms which one you have.
What is leiomyosarcoma?
A rare malignant tumor arising from uterine smooth muscle. It can occasionally resemble a fibroid on imaging before surgery, but it is a separate disease.
Should I be concerned if my fibroid is growing quickly?
Rapid growth alone during the reproductive years has not been shown to predict cancer. A new or growing mass after menopause is different and should be evaluated promptly.
How do doctors check for cancer before fibroid surgery?
MRI, sometimes combined with an LDH blood test, flags higher-risk cases. No test rules out leiomyosarcoma with certainty, which is why surgical planning and pathology after removal both matter.
What happens if cancer is found during fibroid surgery?
You would be referred to a gynecologic oncologist for staging and further treatment. This is uncommon, and it is exactly why all removed tissue is analyzed as standard practice.
Medically reviewed by Annie Kim, MD. Last updated: August 2026