Oncology and Veterinary Clinical Pathology, Department of Veterinary Clinical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
Feline soft tissue sarcomas (STS) are a heterogeneous group of cancers originating from connective tissue. According to recently published retrospective data from The Swiss Veterinary Cancer Registry (Graf et al. 2015) mesenchymal tumors were the second most common tissue type and represented 28% of all evaluated tumors and 15% of the skin tumors. The material included both malignant and benign tumors, but the majority were malignant. Data from the Danish Veterinary Cancer Registry revealed that 13% of all malignant feline tumors were sarcomas. The tumors are most often seen in middle aged to older cats. In general the clinical approach to diagnosis and management of STS is similar in dogs and cats and aggressive surgery is still the mainstay of management potentially combined with postsurgical radiation and/or chemotherapy. During the past 25 years the majority of STS publications in cats are reports on feline injection site sarcomas (ISS) and only limited information is available on non-injection site sarcomas. Feline ISS was first reported in 1991 secondary to rabies vaccination. Since then it has become clear that many types of injections may lead to feline ISS. Immunotherapy using IL-2 injection combined with radiotherapy has recently been registered for use in feline ISS.
Standard of Care?
Work up and diagnosis of feline STS and ISS is similar to the work up of canine STS. Delineation of local disease using advanced imaging procedures (contrast enhanced CT or MRI) is important as palpation alone underestimates the extent of tumor. In addition, routine staging and grading should be performed including a minimum database (complete hemogram including blood smear evaluation, biochemistry, urinalysis) to evaluate the general health of the patient as well as possible paraneoplastic disease, local lymph node evaluation (palpation and tine needle aspirate for cytology), thoracic imaging (X-Rays or CT) to detect pulmonary metastasis, as well as a pre-surgical biopsy for histopathology. Other procedures as relevant for the individual patient.
Therapeutic Management and Prevention
Recommendations have been reported both regarding the therapeutic management and prevention of feline ISS from the European Advisory Board of Cat Diseases (ABCD, Hartmann K, et al. 2015) and regarding vaccination strategies (Vaccine-Associated Feline Sarcoma Task Force (VAFSTF), Vaccination Guidelines Group (VCG) of the World Small Animal Veterinary Association). The most recent guidelines have been published by the ABCD group and are presented below.
European Advisory Board of Cat Diseases (ABCD)
The European Advisory Board of Cat Diseases (ABCD) is a body of experts in immunology, vaccinology and clinical feline medicine that issues guidelines on prevention and management of feline infectious diseases in Europe, for the benefit of the health and welfare of cats. The guidelines are based on current scientific knowledge of the diseases and available vaccines concerned. In 2015 Hartmann K, et al. reported recommendations regarding the management and prevention of feline ISS including reference to the past decades of studies and their levels of evidence. The recommendations are outlined briefly below. The reader is referred to Hartmann et al. 2015 for more detailed information.
ABCD Recommendations Regarding
Therapy: Radical surgery with wide margins at least 3 cm and preferably 5 cm and the removal of one fascial plane under the tumor. This radical approach resulted in complete margins in 88/91 cats in a retrospective study by Phelps et al. 2011. Preoperative or postoperative radiation therapy has been reported to provide some benefit by significantly decreasing recurrence rates and prolonging remission times.
The benefit of chemotherapy is not proven yet and randomized controlled studies have been reported on different immunotherapy approaches which appear promising. One of these therapies, recombinant feline IL-2, has been registered in Europe tor treatment of feline ISS in combination with surgical excision and radiation therapy.
Prevention: Injections in cats should always be given at sites at which surgery would likely lead to a complete cure with the least complicated surgical procedure (such as distal limbs, tail or lateral abdomen). In addition, vaccination should only be performed only as often as necessary and as infrequently as possible. Practitioners and owners should monitor the vaccination site for swelling or lumps and should follow the 3-2-1 rule: Incisional wedge biopsies or total removal for histopathological examination of any mass is warranted if the mass is still present 3 months after vaccination, is more than 2 cm in diameter or is increasing in size one month after vaccination.
On the Horizon
The future diagnosis, management and prognostication of feline ISS likely will likely include biomarkers, molecular diagnostic techniques, molecular imaging (PET-CT, PETMRI), as well as intraoperative methods such as optical coherence tomography (OCT) to delineate tumor and healthy tissues intraoperatively. Furthermore development of specific immune therapeutic approaches are being evaluated and electrochemotherapy studies have been reported which appear promising.
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