Leiomyosarcoma

Leiomyosarcoma is a malignant tumour of smooth muscle. It is seen in various places including the uterus and skin.

General

• Poor prognosis.
• Do not (generally) arise from leiomyomas.
• Often singular, i.e. one tumour; unlike leiomyomas (which are often multiple).

Gross

Features:

• "Fleshy" appearance.
• Necrosis.
• Large size.
• Often singular, i.e. one lesion; leiomyomata are often multiple.

Microscopic

Features:

• Cellular lesion.
• Fasicular arrangement:
  • Whorled look at low power.
  • Groups of spindle cells cut peripendicular to their long axis adjacent to groups of spindle cells cut in the plane of their long axis.
• Features of malignancy (need all three):
  1. Cellular atypia - common.
  2. Necrosis.
     • Should be patchy/multifocal.
       • Zonal necrosis is suggestive of vascular cause.
  3. Mitoses - key feature - definitions suffers from HPFitis:
     • 10 mitoses/HPF.
     • 5 mitoses/HPF - if epithelioid.
     • 2 mitoses/HPF - if myxoid.
     • >=1 mitosis/HPF - if cutaneous.

IHC

• CD10 -ve (important in the context of uterine lesions -- +ve in endometrial stromal sarcoma).
• Positive for SMC markers.
  • Desmin - present in all three types of muscle.
  • Caldesmon.
  • Smooth muscle myosin.

See also

• Soft tissue lesions.
• Uterine tumours.