FELINE VACCINE ASSOCIATED SARCOMAS: 35 CASES.

Purpose: The purpose of this study was to determine the utility of contrast enhanced computed tomography (CT) in the evaluation and treatment of cats with vaccine associated sarcomas. Presentation at a referral institution is often following intervention after one or more previous surgical resections. In the current study a CT scan was performed prior to therapy to determine the extent of disease at initial presentation in comparison to physical examination findings, and to evaluate the utility of imaging in treatment decisions.

Methods: 35 cats with a presumptive or biopsy proven diagnosis of vaccine associated sarcoma that presented to the University of California Veterinary Medical Teaching Hospital were entered into the study. Vaccine history was obtained. Physical examination included caliper measurements of the tumor in 3 dimensions. All cats had complete blood work (complete blood cell count, chemistry panel, and urinalysis), T4, Felv and FIV tests, three view thoracic radiographs, biopsy with routine histopathology, and a CT scan. CT scans were conducted using a General Electric 9800 scanner. A series of 3 mm contiguous axial images were acquired through the mass using a soft-tissue software algorithm prior to administration of contrast medium. Conray® 400 contrast medium was administered intravenously as a bolus at 1 cc/lb and repeat CT evaluation was immediately performed. Tumor measurements were obtained based on physical examination and pre- and post-contrast CT images. Tumor volume was measured as the product of three dimensions multiplied by /6. Additional information abstracted from the CT images included characterization of tumor appearance, number of muscles involved, and whether or not there was evidence of bone involvement.

Results: Age ranged from 4-15 years (median = 10), and there were 21 FS, and 14 MC. Breeds included 22 DSH, 5 DMH, 4 Siamese mix, 3 DLH, and 1 Himalayan. Body weight ranged from 2.9-7.3 kg (median = 5 kg). Tumor appearance on CT included a contrast enhancing mass with a centrally necrotic appearing region and peripherally tendrils of contrast enhanced tissue with extension into the surrounding normal tissue. The number of muscles involved based on the post-contrast CT images ranged from 1-22 (median = 7). Based on caliper measurements the tumor volume ranged from 1.4-281.1 cm³ (median = 23.4, mean = 46.6). The pre-contrast tumor volume ranged from 1.6-384.2 cm³ (median = 44.7, mean = 75.6). The post-contrast tumor volume measurements ranged from 1.8-442.1 cm³ (median = 57.2, mean = 91.7). The tumor volume was larger based on physical examination measurements than the pre-contrast images in 2 cats, and both the pre- and post-contrast CT images in 3 cats. For the remaining 30 cats the pre- and post-contrast tumor volumes were greater than the volume determined based on physical examination. None of the cats had evidence of bone involvement. On histopathology the tumors were diagnosed as fibrosarcoma (n=30) or sarcoma (n=3); results are pending for 2 cats.

Discussion: Contrast enhanced CT images were useful in determining the full extent of disease. Recommendations were often altered based on the CT images and included pre-operative radiation therapy and surgery when surgery alone was deemed inadequate to effect local tumor control, alterations in the surgical approach to include resection of additional muscles and/or bone, and chemotherapy alone as palliative therapy. Acknowledgement: This work was supported by a grant from the Vaccine Associated Feline Sarcoma Task Force.

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