What is cutaneous squamous cell carcinoma in cats?

Squamous cell carcinoma (SCC) is the third most common tumor to affect the skin following basal cell tumors and mast cell tumors. Cutaneous (skin) SCC originates from squamous cells in the skin, and cats of any breed can be affected. 

Cats that are predisposed to SCC of the skin include: 

• Cats with unpigmented (white) or lightly pigmented skin of the face and ears (pinna)
• Cats that spend time outdoors in a sunny climate
  

In general, SCC tends to cause local disease but does 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.

What are signs of squamous cell carcinoma?

SCC in cats can be variable in appearance. 

• Initial growth can look like a scab or a red, thickened area of skin.
• Tumors slowly progress to ulcerations in the skin.
  
• Some tumors can be more proliferative (mass-like) and look like a raised growth whereas others will look more red, flat, plaque-like or ulcerated.
  
• Lesions may be painful on palpation and some cats may traumatize (lick or scratch) the lesions. 
  

Cats are more likely to develop tumors on the face and pinna of the ears, but any skin site can be affected. Cats should be prevented from licking or bothering the tumors to avoid further damage to the tissue and to avoid infection within the tissues.

How is a diagnosis of squamous cell carcinoma made?

A tumor biopsy is usually required to determine 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.

How is squamous cell carcinoma treated?

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 (limited to 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 (Bowen’s disease), 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.

What is the prognosis for a cat with cutaneous squamous cell carcinoma?

In most cats with cutaneous SCC, the prognosis following local therapy (surgery or radiation therapy) is excellent. For large, more invasive lesions, the long-term prognosis is poor if the tumor cannot be removed, but most cats can be made comfortable for 6-12 months with palliative therapy.

Edited By:
Christine Swanson, DVM, DACVIM (Oncology)
April, 2020