Uterine leiomyosarcoma vs leiomyoma
- Lesion
A rare, malignant smooth-muscle tumour of the uterus that arises on its own, not from a fibroid; three microscopic features separate it from one.
What it is
Leiomyosarcoma is the most common pure uterine sarcoma but is rare, arising de novo rather than from a leiomyoma, usually in postmenopausal women. It is diagnosed by combining three features in spindle-cell tumours: tumour (coagulative) necrosis, moderate to severe nuclear atypia and a high mitotic count. Tumours with only one worrying feature that do not meet criteria are called smooth-muscle tumours of uncertain malignant potential. Leiomyosarcomas have complex genomes, spread by blood to the lungs, and have a poor prognosis.
Structure
- Spindle cells in fascicles with enlarged, hyperchromatic, pleomorphic nuclei.
- Tumour cell necrosis: an abrupt transition from viable to dead tumour cells without intervening granulation tissue, unlike the hyaline infarct of a degenerating fibroid.
- Numerous and abnormal mitoses; infiltrative margins and vascular invasion may be seen.
Step by step
- A myometrial cell acquires inactivation of tumour suppressors such as TP53 and RB1.
- Chromosomal instability produces a highly abnormal genome.
- The tumour grows rapidly with necrosis and invades the myometrium and vessels.
- Tumour cells enter veins and seed the lungs and other organs.
Leiomyoma, uncertain potential and leiomyosarcoma
| Feature | Leiomyoma | Smooth-muscle tumour of uncertain malignant potential | Leiomyosarcoma |
|---|---|---|---|
| Number and size | Often multiple, variable | Usually single | Usually single and large |
| Gross | Firm, white, whorled, well circumscribed | Variable | Soft, fleshy, haemorrhagic, necrotic |
| Tumour necrosis | Absent (hyaline infarcts may occur) | Only one worrying feature or borderline values | Present in most |
| Atypia | None or bizarre cells only | As above | Moderate to severe, diffuse |
| Mitoses | Few | As above | Many, often abnormal |
| Behaviour | Benign | Usually benign, small recurrence risk | Malignant, lung metastases |
Markers
- Desmin, smooth-muscle actin, h-caldesmon
- p53 and p16 often aberrant
- Ki-67 high
Clinical notes
- Presents with bleeding, a rapidly enlarging uterus or a pelvic mass in an older woman; growth of a fibroid after menopause is a warning sign.
- Because a sarcoma can be mistaken for a fibroid, uncontained morcellation of presumed fibroids risks spreading an unsuspected sarcoma.
Test yourself
Think of the answer, then tap the question to see it.
Does leiomyosarcoma usually arise from a pre-existing leiomyoma?
No; it arises de novo, and transformation of a fibroid is exceptional.
Which three features are used to diagnose uterine leiomyosarcoma?
Tumour cell necrosis, moderate to severe nuclear atypia and a high mitotic count; at least two are needed in the usual spindle type.
Where does uterine leiomyosarcoma usually metastasize?
Through the blood, most often to the lungs.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Uterine Sarcoma Treatment (PDQ®)–Health Professional Version (National Cancer Institute, 2026); Uterine Leiomyomata (StatPearls (NCBI Bookshelf), 2026).
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Representative model, for educational purposes only.