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:

• Usu. cellular lesion.
• Fasciclar 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. Nuclear atypia.
  2. Tumour cell necrosis.
     • Should be patchy/multifocal.
       • Zonal necrosis is suggestive of vascular cause.
  3. Mitoses - key feature - definitions suffer from HPFitis:
     • >=10 mitoses/HPF - if spindled.
     • >=5 mitoses/HPF - if epithelioid.
     • >=2 mitoses/HPF - if myxoid.
     • >=1 mitosis/HPF - if cutaneous.

Images:

• Uterine:
  • Uterine leiomyosarcoma 1 (WC).
  • Uterine leiomyosarcoma 2 (WC).
• Cutaneous:
  • WC:
    • Cutaneous leiomyosarcoma - intermed. mag. - shows fascicular pattern (WC).
    • Cutaneous leiomyosarcoma - intermed. mag. (WC).
    • Cutaneous leiomyosarcoma - high mag. (WC).
  • www:
    • Cutaneous leiomyosarcoma (upmc.edu).

Subtypes

Major variants:

• Spindled leiomyosarcoma (leiomyosarcoma NOS) - see above.
• Epithelioid leiomyosarcoma.
• Myxoid leiomyosarcoma.

Minor variants:

• Leiomyosarcoma with prominent intravascular growth.
• Leiomyosarcoma with osteoclast-type cells.
• Leiomyosarcoma with clear cells.
• Leiomyosarcoma with xanthoma-type cells.

Epithelioid leiomyosarcoma

Features:

• >50% epithelial appearance.
• >=5 mitoses/HPF - definition suffers from HPFitis.

Myxoid leiomyosarcoma

Features:

• >=2 mitoses/HPF - definition suffers from HPFitis.
• May have minimal nuclear atypia.

IHC

Features:

• Positive for SMC markers.
  • Desmin - present in all three types of muscle.
  • H-caldesmon.
  • Smooth muscle myosin.
• CD10 -ve.
  • May be +ve.
  • Some use in the context of uterine lesions -- CD10 +ve in endometrial stromal sarcoma.

Others:

• ER, PR, AR +ve -- 30-40% of the time.
• CD117 +ve/-ve.
• p53 +ve.
• MIB-1 high.
• Kertins usu. -ve -- more often +ve in epithelioid variant.

See also

• Soft tissue lesions.
• Uterine tumours.
• Leiomyoma.