Uterine leiomyomas (fibroids) are the most common pelvic tumor in women [1,2]. They are benign monoclonal tumors arising from the smooth muscle cells of the myometrium. The pathogenesis of leiomyomas is not well understood. Genetic predisposition, environmental factors, steroid hormones, and growth factors important in fibrotic processes and angiogenesis all play a role in the formation and growth of uterine fibroids . The disease is heterogeneous and different fibroids may have different etiologies; many may have multifactorial pathogenesis . Leiomyoma-related effects on the function and structure of the endometrium are the final common pathways in the pathogenesis of excessive bleeding in myomatous uteri and there is evidence of both histological changes in the endometrium and endometrial vasculature in these uteri [5,6].
The pathogenesis of uterine leiomyomas is reviewed here. The diagnosis and management of leiomyomas as well as variants of leiomyomas are discussed separately. (See "Epidemiology, clinical manifestations, diagnosis, and natural history of uterine leiomyomas (fibroids)" and "Overview of treatment of uterine leiomyomas (fibroids)" and "Variants of uterine leiomyomas (fibroids)".)
Uterine leiomyomas are benign monoclonal tumors arising from the smooth muscle cells of the myometrium. They contain a large amount of extracellular matrix (ECM, collagen, proteoglycan, fibronectin) and are surrounded by a thin pseudocapsule of areolar tissue and compressed muscle fibers.
Leiomyomas are benign lesions. However, there is a heterogeneous group of lesions which have some, but not all, characteristics of malignant disease termed leiomyoma variants. Leiomyoma variants are classified as benign or malignant based upon histologic features. Some leiomyoma variants have histologic findings that make it difficult to define them as benign or malignant (eg, smooth muscle tumors of uncertain malignant potential). This is discussed in detail separately. (See "Variants of uterine leiomyomas (fibroids)", section on 'Smooth muscle tumors of uncertain malignant potential'.)
At least two distinct components contribute to leiomyoma development: