Sarcoma In Uterine Fibroids and Fibroids: What to Know

Uterine fibroids (also called leiomyomas or myomas) are very common, benign growths of the uterine muscle. By age 50, the majority of women will have at least one fibroid. Uterine sarcomas, by contrast, are rare cancers that form in the muscles or connective tissues of the uterus. Because fibroids and sarcomas can cause similar symptoms—such as abnormal bleeding or pelvic pressure—many people worry that a fibroid might “turn into” cancer. Here’s what the evidence shows and how to approach symptoms, diagnosis, and treatment safely.

Key Takeaways

• Fibroids are benign; uterine sarcomas are rare cancers. Most fibroids do not become cancer.
• Current data suggest the chance of an unexpected uterine sarcoma in surgery for presumed fibroids is low, estimated between about 1 in 770 and less than 1 in 10,000 procedures, depending on age and study design.
• No preoperative test can reliably rule out uterine sarcoma. Suspicious features guide decisions but diagnosis is usually confirmed after surgery by pathology.
• New or worsening symptoms—especially after menopause—should be evaluated promptly. Care from a gynecologist (and a gynecologic oncologist if cancer is suspected) is recommended.

Fibroids vs. Uterine Sarcoma: What’s the Difference?

Fibroids are noncancerous tumors made of smooth muscle and connective tissue. They can vary in size and number and often cause no symptoms. When symptoms occur, they may include heavy menstrual bleeding, pelvic pressure, urinary frequency, constipation, pain with intercourse, or difficulty getting pregnant. Trusted overviews are available from the National Institutes of Health and ACOG (the American College of Obstetricians and Gynecologists).

Uterine sarcomas are malignant tumors, most commonly leiomyosarcoma (LMS), endometrial stromal sarcoma (ESS), and undifferentiated uterine sarcoma. These cancers are rare and are biologically distinct from benign fibroids. Importantly, most uterine sarcomas arise de novo—they do not develop from a pre-existing fibroid.

How Common Is Cancer When Fibroids Are Suspected?

In 2014, the U.S. Food and Drug Administration (FDA) drew attention to occult (unexpected) uterine sarcoma in women undergoing surgery for presumed fibroids. Early estimates suggested approximately 1 in 350 procedures might uncover an unsuspected sarcoma. Subsequent analyses, including those summarized by ACOG, indicate the risk is lower overall and varies by age, with pooled estimates ranging from about 1 in 770 to less than 1 in 10,000 surgeries for presumed leiomyomas.

Key point: while the chance of occult sarcoma is low, it is not zero, and this uncertainty influences surgical planning and counseling—particularly regarding techniques that might spread undiagnosed cancer (for example, power morcellation).

Symptoms That Merit Prompt Evaluation

• Heavy or prolonged menstrual bleeding, bleeding between periods, or any new vaginal bleeding after menopause
• Pelvic pain or pressure that is rapidly worsening
• A mass that seems to grow quickly, especially after menopause
• Unexplained anemia, fatigue, or weight loss

These symptoms do not mean cancer is present—fibroids commonly cause several of them—but they warrant timely assessment.

Who Is at Higher Risk for Uterine Sarcoma?

• Age: risk increases with age; postmenopausal status is a red flag when new growth is seen
• Prior pelvic radiation
• Long-term use of tamoxifen
• Rare hereditary syndromes such as hereditary leiomyomatosis and renal cell cancer (HLRCC)

Most people with fibroids will never develop a sarcoma. Having fibroids alone is not considered a strong risk factor for uterine sarcoma.

How Do Clinicians Evaluate a Possible Sarcoma?

There is no single test that definitively distinguishes fibroids from sarcoma before surgery. Clinicians typically use a combination of:

• Clinical history and exam: symptom pattern, growth rate, and menopausal status
• Imaging: ultrasound is first-line; MRI can provide additional detail. Features such as irregular borders, areas of necrosis, or atypical vascular patterns can raise suspicion but are not diagnostic.
• Endometrial sampling: may rule out endometrial causes of bleeding but often misses leiomyosarcoma, which arises in the muscle wall.
• Blood tests: there is no validated blood marker that reliably detects uterine sarcoma.

Definitive diagnosis is made by pathology review of tissue after surgical removal. When preoperative concern for sarcoma is high, referral to a gynecologic oncologist is appropriate.

Treatment Paths: Fibroids vs. Sarcoma

Fibroids (Benign)

• Watchful waiting for small or minimally symptomatic fibroids
• Medications to control bleeding or shrink fibroids: hormonal IUD, combined hormonal contraception, tranexamic acid, GnRH agonists/antagonists (short-term), and newer oral GnRH antagonist combinations approved by the FDA
• Procedures for symptom relief or fertility preservation: uterine artery embolization, radiofrequency ablation, myomectomy
• Hysterectomy for definitive treatment when appropriate

Surgical technique matters. The FDA advises that power morcellation should be used only with legally marketed containment systems and avoided in patients who are postmenopausal or candidates for tissue removal intact through the vagina or a mini-laparotomy, due to the risk of disseminating an unsuspected cancer.

Uterine Sarcoma (Malignant)

• Primary treatment is typically surgery (usually hysterectomy with removal of the tumor intact, without morcellation)
• Depending on type and stage, additional therapy may include radiation or chemotherapy
• Care is best coordinated with a gynecologic oncologist
• Follow-up surveillance is essential because some sarcomas have a risk of recurrence

Minimizing Risk and Making Informed Decisions

• Ask about your individualized risk based on age, imaging, symptoms, and medical history.
• Discuss all treatment options, including nonsurgical choices when reasonable.
• For surgery, review how tissue will be removed, the pros and cons of minimally invasive approaches, and measures to avoid spreading an undiagnosed cancer.
• Seek a second opinion—especially if rapid growth occurs after menopause or imaging looks atypical.

When to Call Your Clinician

Contact your clinician if you experience new postmenopausal bleeding, rapidly enlarging uterine mass, severe or worsening pelvic pain, or signs of anemia (fatigue, shortness of breath, dizziness). Sudden severe pain with fever may indicate a different urgent problem and warrants prompt care.

Trusted Sources and Further Reading

• National Cancer Institute (NCI): Uterine Sarcoma Treatment (PDQ)
• American College of Obstetricians and Gynecologists (ACOG): Uterine Fibroids FAQ
• ACOG Committee Opinion on Morcellation: Uterine Morcellation for Presumed Leiomyomas
• U.S. Food and Drug Administration (FDA): Safety Communication on Power Morcellation
• NIH/NICHD: What Are Uterine Fibroids?

This article is for general education and does not replace personalized medical advice. If you’re concerned about your symptoms or imaging results, consult your clinician for an evaluation and a care plan tailored to you.