Canis ISSN: 2398-2942

Leiomyoma / leiomyosarcoma

Contributor(s): Susan North, Isabelle Desmas-Bazelle


  • Tumors of smooth muscle, therefore can arise at any body site where there is smooth muscle; major locations recognized in the dog are:
    • Female reproductive tract:
      • Most uterine tumors are mesenchymal in origin.
      • ~90% of uterine tumors are leiomyomas.
      • Leiomyosarcomas are the most common malignant tumor of the uterus and vagina.
      • Vulvar/vaginal tumors are largely leiomyomas (83%).
    • Gastrointestinal tract:
      • Most common locations are the jejunum and cecum.
    • Spleen/liver.
    • Subcutaneous tissues.
    • Anecdotal locations: urinary tract, esophagus, pericardium, oral cavity, vessel wall, kidney.
  • Signs: depends on location:
    • Vomiting.
    • Weight loss.
    • Inappetence.
    • Collapse, lethargy.
    • Fecal tenesmus, occasionally visible mass.
  • Diagnosis: imaging; rectal/vaginal examination,cytology and/or histopathology.
  • Treatment: surgery +/- chemotherapy +/- radiotherapy.
  • Prognosis: depends on tumor type and location; vaginal/uterine leiomyomas good prognosis; intestinal/splenic leiomyosarcomas guarded prognosis.


Predisposing factors

  • Early reports (1983) indicated association with female endocrine system in development of vaginal leiomyomas.


  • Major locations of leiomyosarcomas are small intestine (jejunum and cecum), also gastric, spleen and hepatic; intestinal mass usually discrete and easily palpable.
  • Vaginal mass usually palpable per rectum and may be visible especially when animal strains.
  • Leiomyoma of the vagina and vulva are often pedunculated and protrude outside the vulva. They are usually hormonally dependent.
  • Intestinal/gastric leiomyosarcomas metastasise to the liver primarily.
  • Subcutaneous masses are pseudocapsulated masses that have poorly defined histologic margins and may infiltrate alongside and/or through fascial planes.


  • Weeks to months.
  • Present when tumors are causing other clinical signs, eg tenesmus with vaginal tumors Vaginal neoplasia, collapse/anemia with intestinal tumors.
  • Metastasis hematogenously. The metastatic rate for hepatic leiomyosarcoma is 100% for any other abdominal location it is 50% and less than 20% for subcutaneous masses.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Dailey AA, Erhart E J, Duval D L, Bass T, Powers B E (2015) DOG1 is a sensitive and specific immunohistochemical marker for diagnosis of canine gastrointestinal stromal tumors. J Vet Diagn Invest 27 (3), 268-277 PubMed.
  • Sathya S, Linn K (2014) Regression of a vaginal leiomyoma after ovariohysterectomy in a dog: a case report. JAAHA 50 (6), 424-428 PubMed.
  • Maas C P, ter Haar G, van der Gaag I, Kirpensteijn J (2007) Reclassification of small intestinal and cecal smooth muscle tumors in 72 dogs: clinical, histologic, and immunohistochemical evaluation. Vet Surg 36 (4), 302-313 PubMed.
  • Russell K  N, Mehler S J et al (2007) Clinical and immunohistochemical differentiation of gastrointestinal stromal tumors from leiomyosarcomas in dogs: 42 cases (1990-2003). JAVMA 230 (9), 1329-1333 PubMed.
  • Heng H G, Lowry J E, Boston S, Gabel C, Ehrhart N, Gulden S M (2006) Smooth muscle neoplasia of the urinary bladder wall in three dogs. Vet Radiol Ultrasound 47 (1), 83-86 PubMed.
  • Boy S C, van Heerden W F P & Steenkamp G (2005) Diagnosis and treatment of primary intraoral leiomyosarcomas in four dogs. Vet Rec 156 (16), 510-513 PubMed.
  • Liu S M, Mikaelian I (2003) Cutaneous smooth muscle tumors in the dog and cat. Vet Pathol 40 (6), 685-692 PubMed.
  • Kapatkin A S et al (1992) Leiomyosarcoma in dogs - 44 cases (1983-1988). JAVMA 201 (7), 1077-1079 PubMed.
  • Gibbons G C & Murtaugh R J (1989) Caecal smooth muscle neoplasia in the dog - report of 11 cases and literature review. JAAHA 25 (2), 191-197 VetMedResource.
  • Bruecker K A & Withrow S J (1988) Intestinal leiomyosarcomas in six dogs. JAAHA 24 (3), 281-284 VetMedResource.

Other sources of information

  • Vail D M, Withrow S J, Page R L (2013) Cancer of the gastrointestinal tract. In: Small Animal Clinical Oncology. Withrow S J & MacEwen E G (eds), 5th edn. W B Saunders: Philadelphia. pp 356-369.
  • Withrow & MacEwan Paraneoplastic syndromes. In: Small Animal Clinical Oncology. Current Veterinary Therapy XII.