Uterine fibroids are common, non-cancerous growths that develop in the uterus. They are almost always benign. The primary concern is distinguishing them from leiomyosarcoma, a very rare uterine cancer that generally arises independently rather than from existing fibroids.
What Uterine Fibroids Are
Uterine fibroids, also known as leiomyomas, are muscular tumors that grow within the wall of the uterus. They are composed of smooth muscle and fibrous connective tissue. Fibroids can vary significantly in size, from tiny, unseen growths to large masses that can fill the entire uterus.
These growths are classified by their location within or on the uterus. Intramural fibroids grow within the muscular wall, submucosal fibroids are located just beneath the inner uterine lining, and subserosal fibroids develop on the outer surface. Some fibroids can also be pedunculated, meaning they attach to the uterus by a stalk. Uterine fibroids are highly prevalent, affecting an estimated 50% to 70% of women by menopause, with higher rates observed in Black women.
Uterine Fibroids and Cancer Risk
Fibroids are almost always benign; they rarely transform into cancer. Less than 1% of uterine tumors are a rare type of cancer called leiomyosarcoma (LMS). Leiomyosarcoma is an aggressive cancer that typically originates de novo from the uterine muscle tissue, rather than from a pre-existing benign fibroid.
Having fibroids does not increase the likelihood of developing leiomyosarcoma or other forms of uterine cancer. While both fibroids and leiomyosarcomas originate from the uterus’s smooth muscle cells, their cellular characteristics and growth patterns differ significantly. Leiomyosarcomas are characterized by rapid, often infiltrative growth, and specific microscopic features that distinguish them from benign fibroids.
The rarity of leiomyosarcoma is notable, with an annual incidence of approximately 0.35 to 0.64 cases per 100,000 women. This contrasts sharply with the widespread occurrence of benign fibroids. The challenge lies in the similar clinical presentations of both conditions, which often include symptoms such as abnormal bleeding or pelvic pain.
Identifying Concerning Symptoms
Many individuals with uterine fibroids experience no symptoms. When symptoms do occur, they frequently involve heavy or prolonged menstrual bleeding, pelvic pressure or pain, and increased urinary frequency. These symptoms are generally due to the fibroids’ size, number, and location within the uterus.
Certain rare symptoms may raise a question about a more serious condition like leiomyosarcoma. These include unusually rapid uterine growth, especially after menopause, or new onset of vaginal bleeding after menopause. Severe and sudden pelvic pain that is not typical for fibroids could also be a sign. While these indicators warrant prompt medical evaluation, they are more often associated with benign changes within fibroids or other conditions rather than cancer.
Diagnosis and Management
Healthcare providers often detect uterine fibroids during a routine pelvic examination, where they may feel an irregular or enlarged uterus. Imaging techniques are then used to confirm the diagnosis and assess the fibroids. An ultrasound is typically the first imaging method, providing images of the uterus and identifying fibroids. In some cases, a magnetic resonance imaging (MRI) scan may be performed for a more detailed assessment, particularly to help distinguish between fibroids and rare sarcomas.
Distinguishing between a benign fibroid and a rare leiomyosarcoma can be challenging before surgical removal, as their symptoms can overlap. Imaging features such as irregular margins, rapid growth (especially post-menopause), and specific signal characteristics on MRI can raise suspicion for sarcoma. However, a definitive diagnosis of leiomyosarcoma is typically made after surgical removal of the mass and subsequent pathological examination of the tissue.
Management approaches for benign fibroids vary based on symptoms, fibroid size and location, and patient preferences, including fertility plans. Options range from watchful waiting for asymptomatic fibroids to medications that help manage symptoms like heavy bleeding or temporarily shrink fibroids. Surgical procedures, such as myomectomy (to remove fibroids while preserving the uterus) or hysterectomy (for complete uterus removal), are also options. For leiomyosarcoma, treatment is generally more aggressive, often involving surgery, which may be followed by radiation therapy or chemotherapy.