Are uterine fibroids a precancerous condition for endometrial cancer?

Uterine Fibroids and Endometrial Cancer Risk

Uterine fibroids are not considered precancerous lesions for endometrial cancer, though postmenopausal women with fibroids and abnormal bleeding should be evaluated for malignancy due to age-related risk factors rather than the fibroids themselves. 1

Relationship Between Fibroids and Endometrial Cancer

The evidence regarding the relationship between uterine fibroids and endometrial cancer is mixed:

• According to the American College of Radiology's 2024 guidelines, fibroids are benign smooth muscle tumors that typically shrink after menopause due to decreased estrogen levels 1
• Postmenopausal bleeding in women with fibroids warrants evaluation for endometrial cancer, but this is due to age-related risk factors rather than the fibroids being precancerous 1
• The risk of malignancy in women with presumed fibroids increases with age (from 2.94 per 1,000 overall to 10.1 per 1,000 in women aged 75-79) 1

Evidence Against Fibroids Being Precancerous

Several studies suggest fibroids are not precancerous for endometrial cancer:

• A 2020 case-control study found that women with a history of clinically diagnosed uterine fibroids actually had lower odds of developing endometrial cancer compared to controls (odds ratio: 0.148,95% CI: 0.097,0.225) 2
• A 2022 population-based study found no evidence of higher risk of uterine malignancy in women with uterine fibroids confirmed by myomectomy 3

Evidence Suggesting Possible Association

Some evidence suggests a potential association:

• A 2011 population-based case-control study found that self-reported history of uterine fibroids was associated with an increased risk of endometrial cancer (OR=1.39; 95% CI: 1.10-1.74), particularly in women with normal BMI and premenopausal women 4

Risk Factors for Endometrial Cancer

The established risk factors for endometrial cancer include:

• Obesity (RR 2.54 for obese women) 1
• Hypertension (RR 1.81) 1
• Diabetes mellitus (OR 2.1) 1
• Nulliparity and infertility 1
• Polycystic ovarian syndrome (OR 2.79-2.89) 1
• Unopposed estrogen therapy (10-30 fold increased risk with 5+ years of use) 1
• Early menarche/late menopause 1
• Tamoxifen use (RR 2.53, higher in postmenopausal women) 1
• Lynch syndrome genetic mutations 1

Clinical Implications

For women with uterine fibroids:

• Routine screening for endometrial cancer is not recommended in asymptomatic women with fibroids 1
• Postmenopausal women with fibroids and abnormal uterine bleeding should undergo endometrial biopsy to rule out endometrial cancer prior to any interventional treatment 1
• Continued fibroid growth or bleeding after menopause should raise suspicion for uterine sarcoma rather than endometrial cancer 1
• The natural history of fibroids is typically shrinkage after menopause due to decreased estrogen levels 1

Important Distinctions

It's important to distinguish between different uterine malignancies:

• Endometrial cancer arises from the endometrial lining
• Uterine sarcomas (including leiomyosarcomas) arise from the myometrium or connective tissue
• Recent evidence suggests leiomyosarcomas do not arise from malignant transformation of fibroids 3

While monitoring women with fibroids is appropriate, this is primarily to detect symptoms requiring treatment rather than because fibroids are considered precancerous for endometrial cancer.