The term malignant mesenchymoma has been applied to sarcoma that exhibit two or more lines of specialized differentiation. They are an uncommon soft tissue tumors first described by Stout in 1948.
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, kidney, spleen) and bone.
Malignant mesenchymoma usually occur as a finite mass but concurrent mixed mesenchymal tumors such as fibrosarcoma, rhabdomyosarcoma, liposarcoma, osteosarcoma and chondrosarcoma have also been reported.
Metastases are common, with regional vasoinvasion and hematogenous spread to the lungs.
Diagnosis is based primarily on histological examination of biopsied tissue.
Treatment usually requires debulking surgery with adjuvant radiation therapy.
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