Malignant mesenchymoma

From Dog

Malignant mesenchymoma are a neoplastic soft-tissue sarcoma of dogs derived from mesenchymal tissues such as bone, cartilage, fat, muscle, vascular or hematopoietic tissues[1].

The term malignant mesenchymoma has been applied to sarcoma that exhibit two or more lines of specialized differentiation[2]. They are an uncommon soft tissue tumors first described by Stout in 1948[3].

Although these tumors have been reported in young dogs, they primarily affected geriatric patients, with tumors predominantly involve retroperitoneum and chest wall, but also visceral organs (liver, heart[4], kidney[5], spleen[6]) and bone.

Malignant mesenchymoma usually occur as a finite mass but concurrent mixed mesenchymal tumors such as fibrosarcoma, rhabdomyosarcoma, liposarcoma, osteosarcoma and chondrosarcoma[7] have also been reported.

Metastases are common, with regional vasoinvasion and hematogenous spread to the lungs[8].

Hypertrophic osteoarthropathy has been reported as a sequela to this condition due to pulmonary metastases[9], which frequently resolves following surgical removal of the mass or vagotomy.

Diagnosis is based primarily on histological examination of biopsied tissue.

A differential diagnosis would include adenocarcinoma, melanoma, malignant fibrous histiocytoma, fibrosarcoma, leiomyosarcoma and rhabdomyosarcoma.

Treatment usually requires debulking surgery with adjuvant radiation therapy.

These tumors are frequently non-responsive or poorly responsive to chemotherapy but cisplatin and carboplatin has improved survival rates in some dogs[10].


  1. McDonald RK & Helman RG (1986) Hepatic malignant mesenchymoma in a dog. J Am Vet Med Assoc 188(9):1052-1053
  2. Fletcher CD et al (2002) World Health Organization of Tumors. Pathology and Genetics of Tumours of Soft Tissue and Bone. Lyon, France: International agency for research on cancer Press (IARC)
  3. Stout AP (1948) The mixed tumor of mesenchymal derivatives. Ann Surg 127:278–290
  4. Gómez-Laguna J et al (2012) Malignant mesenchymoma of the heart base in a dog with infiltration of the pericardium and metastasis to the lung. J Comp Pathol 147(2-3):195-198
  5. Robison RL et al (1997) Mixed mesenchymal tumor in the kidney of a young beagle dog. Toxicol Pathol 25(3):326-328
  6. Spangler WL et al (1984) Primary mesenchymal (nonangiomatous/nonlymphomatous) neoplasms occurring in the canine spleen: anatomic classification, immunohistochemistry, and mitotic activity correlated with patient survival. Vet Pathol 31(1):37-47
  7. Machida N et al (2003) Primary malignant mixed mesenchymal tumour of the heart in a dog. J Comp Pathol 128(1):71-74
  8. Robinson TM et al (1998) Malignant mesenchymoma associated with an unusual vasoinvasive metastasis in a dog. J Am Anim Hosp Assoc 34(4):295-299
  9. Hahn KA & Richardson RC (1989) Use of cisplatin for control of metastatic malignant mesenchymoma and hypertrophic osteopathy in a dog. J Am Vet Med Assoc 195(3):351-353
  10. Murphy S et al (2006) Intermandibular malignant mesenchymoma in a crossbreed dog. J Small Anim Pract 47(9):550-553