Soft tissue sarcomas

Small Animal Section: No. 14

SOFT TISSUE SARCOMAS OF THE SKIN AND SUBCUTIS OF DOGS

Up to 15% of all skin and subcutaneous tumours in dogs are soft tissue sarcomas. Females and large breed dogs are reportedly predisposed. Tumours are classified according to the cell type of origin and include :

• malignant haemangiopericytoma (vascular pericytes)	• myxozarcomas (myxoid stroma)
• malignant schwannoma (perineural Schwann cells)	• leiomyosarcoma (smooth muscle cells)
• neurofibrosarcoma	• malignant fibrous histiocytoma
• fibrosarcoma	• lymphangiosarcoma
• liposarcoma	• granular cell tumour

Histological morphology : Many of these tumours have similar histological characteristics, and are made up of whorls and sheaves of spindle shaped cells. Particularly in anaplastic and poorly differentiated tumours, morphology alone is not sufficient to make a diagnosis, and since few specific cell markers are available, immunochemistry may not help.

Biological behaviour : Fortunately, the listed tumours all have similar biological behaviour., characterised by a high local recurrence rate and relatively low metastatic potential (17%). Overall, approx 33% of dogs with spindle cell tumours die of tumours related causes. The following three factors have been identified as useful prognostic indicators for soft tissue sarcomas, and a diagnosis od specific cell type may not be necessary, therefore, to make an informed prognosis for the affected dog.

Clean surgical margins	95% of dogs with clean excisional surgical survive beyond 2 years (vs 65% of dogs with neoplastic cells on biopsy margins)
Mitotic rate	Tumours with >20 mitotic figures per high power field (HPF) are 5 times more likely to metastasise than those with fewer mitoses. Dogs with such tumours are 2.5 times as likely to die of tumour-related causes than those with tumours with fewer mitoses. Average survival time for dogs with >20 mitoses/HPF survive on average 2 years.
Degree of necrosis	Dogs with tumours with more than 10% necrotic tissue are 3 times more likely to die of tumour related causes than those with tumours with less necrosis. Overall, approx 33% of dogs with spindle cell tumours die of tumour-related causes.

Site is an important additional prognostic indicator, since none of the dogs in this study with tumours distal to the elbow or knee developed metastasis. This may be because amputation of these tumours is common since wide excision is rarely feasible at these sites.

Treatment : We highly recommend, therefore, taking pre-operative biopsies to determine mitotic rate, and degree of necrosis. This will provide the basis for an assessment of the need for wide or radical excision. Surgical specimens should then be submitted whole for evaluation of the margins. Surgical excision is the treatment of choice. Chemo and radiotherapy alone are not adequate treatment methods, but radiation in combination with surgery or hyperthermia may control lesions that are not amenable to wide surgical excision.

References :

CA Kuntz et. al. (1997) Prognostic factors for surgical treatment of soft tissue sarcomas in dogs : 75 cases. Journal of the American Veterinary Medical Association 211 (9) 1147-1151

Compiled by:

Dr Emily Lane

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Last modified: Friday June 25, 2004