Soft tissue sarcomas (STS) in cats can be naturally occurring or secondary to vaccination. Naturally occurring sarcomas generally have a slow growth rate and low potential (5-15% chance) to metastasize (spread). In contrast, vaccine related sarcomas are locally aggressive with a moderate-high growth rate and are more likely to metastasize (25-30% chance) to the lung and other organs. A complete evaluation of a cat with soft tissue sarcomas includes a CBC, chemistry profile, urinalysis, thoracic radiographs and biopsy. An abdominal ultrasound, CT scan and/or MRI may also be indicated in some cases.
Treatment options include surgery and/or radiation therapy for the primary tumor site, and if the tumor is considered high grade, chemotherapy may be warranted to combat the metastatic potential (spreading). We recommend chemotherapy on a case-by-case basis for patients with vaccine related sarcomas. Surgery is generally the first treatment option and, since local tumor recurrence is common if the tumor is incompletely or narrowly excised, wide surgical margins are recommended. Patients with a wide-complete excision can experience long term local control; therefore, a CT scan or MRI may be advised prior to surgery to further assess the tumor extent in order to achieve a wide/complete excision. Cats undergoing surgical excision of naturally occurring soft tissue sarcomas can have long term local control (possibly a cure); however, surgical excision of vaccine related sarcomas is more difficult due to tumor infiltration and the more aggressive nature of these tumors.
If the surgical excision is incomplete (tumor cells extend to the surgery edge) or narrow, tumor recurrence is likely. In situations where more surgery isn’t possible radiation therapy is advised as a follow-up to surgery to prevent local tumor recurrence. Radiation may also be used before surgery for larger tumors, where surgery may not be reasonable, in hopes of reducing the tumor size and making surgery an option. Radiation therapy generally involves 15-17 treatments administered on a Monday through Friday schedule. The patient undergoes a short-acting anesthetic period per treatment in order to keep the patient still since we cannot be in the room with them during treatment. Patients tolerate the protocol well but do develop side effects towards the end of the protocol that resolve several weeks after completing treatment. The side effects depend on the region treated but may include redness of the skin, hair loss and dry dermatitis. Most cats do not experience moist dermatitis such as a “burn” secondary to radiation. Studies indicate average tumor control/survival rates of 1.5-3 years when the combination of surgery and radiation is used for vaccine related sarcomas. These reports are limited and should improve with aggressive treatment at the time of first occurrence. Less information is known regarding the combination of surgery and radiation for naturally occurring sarcomas. Radiation can also be used as the primary treatment when surgery is not an option but this has not been very effective in providing long term control especially for vaccine related sarcomas. In some situations radiation may decrease the tumor burden making surgery an option.
In addition to radiation and surgery, we may also recommend chemotherapy for cats at high risk for metastatic disease, non-resectable tumors, or those that already have metastatic disease. The use of chemotherapy in these patients may prevent metastatic disease or potentially shrink non-resectable tumors providing palliation or making other treatment options such as surgery and/or radiation possible. A combination protocol of doxorubicin +/- cyclophosphamide is given on an every 3-week schedule for a total of 4 to 6 treatments. Side effects are generally self-limiting but may include weakness/lethargy, poor appetite/anorexia, vomiting and/or diarrhea, decrease in their white blood cell count and rare kidney toxicity.
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