Leiomyoma and leiomyosarcoma of soft tissue
- Lesion
Benign smooth muscle tumours of skin and vessels, and their malignant counterpart, a sarcoma of the retroperitoneum and large veins.
What it is
Outside the uterus, leiomyomas arise from the arrector pili muscles of the skin (pilar leiomyoma), from vessel walls (angioleiomyoma) or from genital smooth muscle. Multiple cutaneous and uterine leiomyomas occur in hereditary leiomyomatosis and renal cell cancer, caused by germline fumarate hydratase mutations. Leiomyosarcoma is a malignant smooth muscle tumour of adults, usually in the retroperitoneum, the deep soft tissue of the limbs and the walls of large veins such as the inferior vena cava; it has complex genetics with frequent TP53 and RB1 loss.
Structure
- Leiomyoma: interlacing fascicles of uniform spindle cells with blunt-ended (cigar-shaped) nuclei and pink fibrillar cytoplasm; no atypia or mitoses.
- Leiomyosarcoma: same fascicular pattern with nuclear atypia, many mitoses and coagulative tumour cell necrosis.
- Immunohistochemistry: smooth muscle actin, desmin and h-caldesmon.
Step by step
- Benign tumours arise from smooth muscle cells of skin, vessels or genital tract; FH loss causes fumarate to accumulate.
- Fumarate inhibits enzymes that degrade HIF, creating a pseudohypoxic state that favours growth.
- Leiomyosarcomas arise with TP53 and RB1 loss and widespread genomic instability.
- Tumours in vessel walls grow along the vein lumen.
- High-grade tumours spread by the blood to lungs and liver.
Markers
- Smooth muscle actin
- Desmin
- h-Caldesmon
- Fumarate hydratase loss (HLRCC)
Clinical notes
- Painful skin nodules in a woman with many early uterine fibroids should raise the possibility of HLRCC, with kidney surveillance for the family.
- Leiomyosarcoma of the IVC can cause leg oedema or Budd-Chiari syndrome.
Test yourself
Think of the answer, then tap the question to see it.
Which germline gene causes multiple cutaneous and uterine leiomyomas with kidney cancer?
FH (fumarate hydratase).
Where does soft tissue leiomyosarcoma typically arise?
In the retroperitoneum, deep limbs and walls of large veins such as the IVC.
Which features separate leiomyosarcoma from leiomyoma?
Nuclear atypia, mitotic activity and tumour cell necrosis.
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: Hereditary leiomyomatosis and renal cell cancer: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2025); Soft Tissue Sarcoma Treatment (PDQ®)–Health Professional Version (National Cancer Institute, 2025).
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Representative model, for educational purposes only.