Clinical history: A 65-year-old female presented with large uterine fibroids, rapidly increasing in size over the last few months.
What is your diagnosis?
Discussion and answer
Microscopically, a spindle cell lesion with necrosis and increased mitotic count (20 per 10 high power field) is seen. The tumour occupies 95% of the myometrium and extends to the serosal surface. While lymphatic invasion is not seen on sections, one lymph node is positive for metastatic disease. Tumour also extends to paraovarian tissues. Tumour cells are muscle specific actin (MSA) and caldesmon positive and negative for CD10, ER and PR. MIB-1 is positive in 20-30% tumour cells.
The diagnosis is leiomyosarcoma. Uterine leiomyosarcomas show: hypercellularity, moderate to marked nuclear atypia, high mitotic rates (>10 per 10 high power fields) and abrupt tumour cell necrosis. Vascular invasion is not common.
The differential diagnosis includes cellular leiomyomas, mitotically active leiomyomas, leiomyomas with necrosis, leiomyomas with bizarre nuclei and endometrial stromal sarcomas.