Page 370 - WSAVA2017
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An Urban Experience
J. Kirpensteijn1
1Hill’s Pet Nutrition, GPVA, Topeka, USA
What is our surgical strategy for soft tissue sarcomas?
Jolle Kirpensteijn, DVM, PhD, Diplomate ACVS & ECVS Hill’s Pet Nutrition
400 SW 8th Avenue, Topeka, Kansas, 66603, USA.
Sarcomas of soft tissues (STS) are common in companion animals and pose a therapeutic and diagnostic challenge for the practising veterinarian. STS is defined as a malignant tumour of the extraskeletal connective tissues. These tissues, all of mesoderm origin, surround, support or connect other anatomic structures and are present in any part of the body.
Because soft tissues are estimated at 40% proportional body weight, it is not surprising that numerous soft tissue tumours arise with regularity. STS form an assembly of tumours of different histogenetic origin, with ubiquitous localisation possibilities, and variation in biological behaviour. Still, STS are often grouped together because of their shared mesodermal origin, similarities in clinical presentation, and communality in diagnostic and therapeutic approach. In general, STS are fleshy (the Greek word ‘Ѕαρκομα’ or ‘sarkoma’ is often translated as flesh-like mass), infiltrative and locally aggressive tumours that have a variable metastatic potential. Mast cell tumours are often soft to the touch and can be either well described or ill defined.
STS are common tumours and comprise from 15% (skin and subcutaneous tissues) to 35% (spleen) of all canine tumours, dependent on original tumour location. Cats are afflicted less frequently (7% reported for skin and subcutaneous tissues). Clinically, STS often are solid masses that seem well circumscribed and encapsulated. However, this is based upon the presence of a pseudocapsule of atrophic remains of surrounding tissue and wedged tumour cells, while infiltration through this pseudocapsule and through fascia leads to attachment to deeper structures. The annual incidence of STS in
the United States is estimated to be 35/100.000 for dogs and 17/10000 for cats at risk. These data are not available for the European countries.
Little is known about the pathogenetic cause of STS in dogs and cats. Changes in genetic make-up, chronic trauma, foreign bodies, vaccinations, parasites and radiation have been associated with STS in both species. P53 mutations and MDM2 gene amplification were observed in a subgroup of canine soft tissue sarcoma; however, familial predispositions have not been reported. No sex or breed predilections have been found, although certain breeds seem to be afflicted with tumours more commonly than others. In general, most studies report medium to large breeds to be affected more commonly, with a overrepresentation of the older animal. The presence of foreign bodies or material (such as vaccinations) may induce chronic stimulation of the tissues and promote neoplastic transformation.
All soft tissues are exposed to the risk of benign or malignant tumour formation. Any classification schedule, however, is complicated by overlapping patterns of dedifferentiation or by the inability to recognize the appearance of the cell of origin. A classification by localisation, grade and tumour stage seems more logical and may prove more useful at present. Advances in histochemical, electron microscopic and biogenetic markers will improve the ease of classification in the future.
The diagnostic plan for STS is not essentially different from any other tumour type. The physical appearance
is noticed depending on the location of the tumour and, in general, peripherally located tumours are more easily detected and often smaller than more centrally located STS. Pain is associated with location, pressure of the tumour or tumour invasion. Some peripheral nerve sheath tumours have been reported to be sensitive to the touch. A clinical differentiation between benign and malignant
is not possible, so additional diagnostics are necessary. Moreover, rate of growth of the tumour often does not predict the biologic behaviour correctly. Additional biopsy specimens should be obtained in all cases. The easiest method of biopsy is fine needle aspiration (FNAB), and this method should be used as the first step in the diagnosis. Although many STS are not well diagnosed
by FNAB because of their limited exfoliative character, many other tumour types can be excluded as well as some inflammatory processes; in particular if infection can be demonstrated while overlying skin is intact. In case
of any doubt, and in particular also if cytology indicates mesenchymal proliferation in absence of an inflammatory response, this provides a solid indication for further diagnostic work-up. Incisional, excisional or thick needle

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