Cat Fibrosarcoma

Fibrosarcomas are a type of soft tissue sarcoma (STS), and in general, this term acts as an umbrella for a variety of tumors including (fibrosarcoma-connective tissue, chondrosarcoma-cartilage, liposarcoma-fat tissue, hemangiosarcoma-blood vessel cells, nerve sheath tumor, hemangiopericytoma-cells supporting blood vessels, malignant fibrous histiocytoma). These tumors range in name based upon their cell type (as above) as well as their aggressiveness. Most tend to be highly invasive into the local tissues, but spread/metastasis into other organs such as the lungs is generally low. High-grade tumors will metastasize in ~25% of cats. These tumors often grow slowly and grow passively along tissue planes.

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STS are often first noted as a lump by the owners that often grow slowly over time. Most often the mass feels fixed to the underlying tissue and its borders are indistinct. The best description of these tumors is an “octopus” in which the head of the octopus is the area of the tumor you can feel but the tumor has tentacles (tendrils) that can go much deeper (up to 2 or 3 inches) out into the surrounding normal tissue. The tendrils of the tumor are actually microscopic cells that are the most active part of the tumor and lead to re-growth when not surgically removed. Patients are staged with chest x-rays and bloodwork (CBC, serum chemistry). These tests allow us to determine if the cancer has spread to other areas in the body, which is dependent on the type/grade of the tumor.

Treatment for STS involves surgery that is often incomplete in removing all cancer cells because of the local microscopic invasiveness of the tumor; however, in cases where a tumor is on a limb, surgery can be curative with an amputation. In cases where the tumor is incompletely removed we recommend either a second surgery (if feasible) or radiation therapy. Studies have shown that following up with radiation therapy can provide excellent local control, however, this depends on the grade of the tumor. In cases where a tumor is a high grade or it is the type of tumor that has a great chance to spread, we often recommend chemotherapy in addition to the local therapy. Most often this entails adriamycin (IV) given once every 3 weeks for 5 times. At the end of the chemotherapy patients are continuously monitored for local recurrence.

The prognosis associated with these tumors depends on the grade and treatment implemented. Without aggressive and complete surgical removal and/or radiation therapy, the majority of tumors recur within a year. However, with complete local control, 50% of cats may survive without tumor recurrence for several years. In cases of high-grade tumors treated with a combination of surgery, radiation therapy, and chemotherapy, there is a 50% chance of survival of 2 years.

If tumors are inoperable, then treatment with radiation and chemo may be considered. Approximately 1/3 of tumors shrink and 1/3 of tumors stabilize for a limited period of time (3-6 months on average). If tumors are considered to be vaccine-induced, treatment with novel chemo agents such as Palladia may be useful.