Smooth Muscle Tumours

Smooth muscle tumours of the uterus may be benign or malignant. Leiomyomata are commonly known as fibroids. Leiomyosarcomas are much rarer.


Leiomyomas are extremely common tumours in women. Exact incidence is not easily obtained.
Leiomyosarcoma usually occurs in older women and is much rarer (1% of uterine tumours).

Aetiology and Pathogenesis

Aetiology is unclear.
Leiomyomas often possess simple chromosomal abnormalities involving the HMGA1 and HMGA2 genes. These are frequently involved in benign neoplasms. Leiomyosarcomas have highly varied karyotypes.

Natural History

Leiomyomas often cause no symptoms and can vary in size from microscopic to massive. They tend not to not invade locally but can interfere with pregnancy.
Leiomyosarcomas invade locally throughout the myometrium and into adjacent structures. Haematogenous spread occurs frequently, most commonly to the lungs. Transcoloemic spread throughout the peritoneum can occur.

Clinical Presentation

Leiomyomas are usually clinically silent but may present with bleeding or be diagnosed incidentally during imaging for other reasons. Large tumours may have central necrosis on imaging.
Leiomyosarcomas may also be clinically silent if localised. Regional disease may lead to obstruction of the urinary or gastrointestinal tracts. Metastatic disease presents with weight loss and symptoms related to the metastatic sites. Rapidly growing myometrial tumours are far more frequently leiomyoma than sarcoma.

Tumour/Normal Tissue Features

Leiomyomas are grey-white in colour and a whorled pattern. This pattern is also seen microscopically, with uniform smooth muscle cells and minimal mitotic figures. Larger tumours may degenerate centrally giving a red (haemorrhagic) or yellow (necrotic) appearance. They are easily shelled out from the surrounding myometrium. Submucosal tumours may form polyps with the lumen of the uterus and occasionally prolapse out through the cervix. They are frequently multiple.
Leiomyosarcomas are usually solitary masses with a fleshy, yellow or red cut surface. They may have patchy areas of necrosis. The average size is 8 cm. Microscopically, the tumours are more cellular than leiomyomas, and the nuclei are hyperchromatic with visible nucleoli. High mitotic rates and areas of necrosis are often visible.

Staging / Classification

TNM or other staging system if relevant



Kumar: Robbis and Cotran Pathologic Basis of Disease
WHO Blue Book - Breast and Female Reproductive System