Feline Squamous Cell Carcinoma
Squamous cell carcinomas (SCC) in cats are tumors occurring in various parts of the body. The tumors commonly arise from squamous epithelial cells within the skin and “wet tissues” of the nose and mouth. Tumors on the skin and ear tips may be solar-induced and it has been postulated that viral infections may be associated with some forms of SCC as well.
The behavior of SCC in cats is varied depending on the location and grade of the tumor with some lesions being slowly progressive over years while other advance rapidly over a course of a few weeks. Metastasis to the lymph nodes and lungs is uncommon occurring in less than 20% of cats. The tumors, however, tend to be locally invasive, may be large and destructive to the bone, and often recur even after aggressive surgical removal. Some tumors are cobblestone in appearance while others are ulcerative.
The treatment of choice for small, superficial lesions is surgical removal. If not possible to remove the entire lesion with a “margin” of normal tissue around the tumor, then radiation therapy may be helpful. For cases of sprawling skin lesions, topical therapy with immunomodulator creams may be helpful, such as Imiquimod, which is used in humans with Bowen’s disease. The prognosis for superficial lesions treated with surgery and/or radiation therapy is favorable. Response rates of 70-80% have been noted with radiation and survival time is often several years. Occasionally additional and/or recurrent tumors develop and must also be treated.
The treatment of choice for large tumors and tumors of the mouth is largely palliative. Various combinations of chemotherapy, radiation therapy and supportive medications have shown transient responses. Chemotherapy is the basis for patients with the metastastic disease. However, SCC is poorly responsive to chemotherapy in these cases and the long-term prognosis for patients with metastatic SCC is guarded with average survival times <6 months.
A newer chemotherapy agent that is used in dogs and some cats is Palladia™. Palladia is produced by Pfizer Inc. and has become the first veterinary therapeutic approved by the FDA to treat mast cell tumors. Unlike traditional chemotherapy, Palladia is a more of a “targeted” chemotherapy agent. The target molecules for this particular drug are VEGFR, PDGFR, and c-kit, all proteins expressed by various cancer cells. Palladia has been shown to reduce/slow the growth of other types of cancer by decreasing a tumors blood supply (by inhibiting both VEGFR and PDGFR) and limiting its nutrients. This means Palladia may have efficacy against a variety of other cancers, especially a large amount of carcinomas.
Palladia is an oral anticancer medication given on an every other day basis at home. Although Palladia is oral and “targeted” in nature, severe side effects can occur if early signs are not detected. The most significant side effects may be GI in nature and include vomiting, nausea, diarrhea, inappetence and weight loss. Additional side effects include a decrease in the white cell count, anemia, and muscle cramping. If caught early and treated aggressively, most side effects are reversible depending on the patient’s clinical status.