Squamous cell carcinoma (SCC) is the third most common tumor to affect the skin following basal cell tumors and mast cell tumors. SCC originates from squamous cells in the skin, and cats of any breed can be affected. However, cats with unpigmented (white) or lightly pigmented skin of the face and ears (pinna) that spend time outdoors in a sunny climate are predisposed to developing SCC. In general, SCC tends to cause local disease but do not metastasize (spread to other sites from the primary site). Cats will commonly develop multiple skin lesions because the sun exposure typically covers a large area of skin.
Signs & Symptoms
SCC in cats can be variable in appearance but often initially look like a scab or a red, thickened area of skin. Lesions may be painful on palpation and some cats may traumatize the lesions. Cats are more likely to develop tumors on the face and pinna of the ears, but any skin site can be affected. Tumors slowly progress to ulcerations in the skin. Some tumors can be more proliferative and look like a mass whereas others will look more like red, flat, plaque lesions.
Usually a tumor biopsy is required for a diagnosis. However, some of the more mass-like lesions may be diagnosed following fine needle aspiration and cytology, where a sample of cells is evaluated.
Treatment & Aftercare
As is true for most tumors, it is best to treat SCC of the skin when lesions are small and not very invasive into the tissue below the top layer of skin. Surgical resection can provide long-term control and even cure in some cats with skin SCC. For cats with SCC on the ear (pinna), removal of the pinna (pinnectomy) may be necessary. For small tumors, alternative treatments include superficial radiation therapy with strontium, which is very well tolerated and effective. Other treatments that may be possible for skin SCC include cryotherapy, photodynamic therapy, laser ablation, and intralesional chemotherapy. For a unique type of skin SCC called Bowenoid carcinoma, which affects multiple sites, a topical medication may be useful. It is important to discuss the various advantages and disadvantages of treatment options with your pet’s veterinary oncologist. Following treatment in cats with suspected sun-induced tumors, monitoring for new skin lesions is essential as cats may develop additional lesions. Limiting sun exposure may be beneficial in the long-term.
In most cats with skin SCC, the prognosis following local therapy (surgery or radiation therapy) is excellent. For large, more invasive lesions, the long-term prognosis is poor but most cats can be made more comfortable for 6-12 months with palliative therapy.
Jessica Lawrence, DVM, DACVIM (Oncology), DACVR (Radiation Oncology), MRCVS, DECVDI (Radiation Oncology)