Squamous Cell Carcinoma (SCC): An Overview
Introduction and Overview:
Squamous cell carcinoma (SCC) is one of the most common skin tumors in both dogs and cats. SCC is the most common tumor of cats appearing on the non-haired part of the nose, called the nasal planum. It is especially common in older cats. SCC may also affect cats’ ears, including the ear canal, and also can be seen around their eyes. Older cats may also have SCC on their feet and toes, although this form of the disease usually is metastatic from an underlying tumor in the lungs. Cats which are light in color (especially white cats) are predisposed to SCC, especially if they spend a lot of time in the sunlight. SCC in cats tends to be locally invasive, but slow to spread.
SCC usually appears as crusting, oozing sores and/or an actual mass on the cat’s face - around the nose, eyes or ears. The cat may scratch at the site of the carcinoma, and there may be an odor or a discharge from the area. The lesion may bleed, and the cat may sneeze more frequently than usual if the nose is affected.
Most veterinarians will draw blood for a complete blood count and a blood chemistry profile when presented with a cat showing the above clinical signs. They also may sample and assess the cat’s urine. With SCC, these tests usually are normal, but it is sensible to perform them to rule out other possible problems. The next test generally is a fine needle aspirate of the mass or site of the crusting or sore. This involves inserting a needle into the lesion and pulling out cells from the site with a syringe. The sample is transferred onto a glass slide and examined under a microscope (this is called “cytology”). While this test can be diagnostic of SCC, sometimes the site may be so inflamed and irritated that interpretation of the sample is difficult. The best test to actually confirm a diagnosis of SCC is a biopsy, which requires sedation and involves taking an actual sample (a “chunk” or “slice”) of the affected tissue. This sample is then sent to a laboratory for assessment by a pathologist.
Other tests that your veterinarian may recommend include a series of thoracic (chest) radiographs (x-rays), to determine whether the carcinoma has metastasized (spread). SCC on the nose, around the eyes and in the ears usually is locally invasive, but metastasis is uncommon. SCC which appears on cats’ toes usually is locally invasive as well. However, unlike the facial form, SCC on the feet of cats normally represents spread of the disease from a primary tumor in the lungs. This is not the case in dogs. Your veterinarian also may suggest an MRI or CT scan of the affected site, to assess possible bone involvement and the extent of the tumor or sore. These tests can also help in the planning of treatment, which might include surgery and/or radiation.
Surgical removal of facial lesions (mass, sore, crusted area), with wide margins, often cures the disease. “Wide margins” means that the veterinarian removes not only the diseased tissue, but also some healthy tissue immediately adjacent to the lesion site. Given the predominance of SCC on cats’ faces, wide margins are often not possible. Surgical removal of a cat’s affected toe is not a very good option, as this form of carcinoma normally reflects metastasis from another primary site (usually the lungs). Even if the affected toe is amputated, the cancer likely will show up in another toe, and eventually the cat will become systemically ill.
Aggressive surgical treatment to excise carcinoma on the nose is an excellent option if the cancer is caught early, is not too extensive and does not involve the mouth/lip or surrounding skin. If wide margins aren’t possible, subsequent radiation treatment of the nose area has proven very helpful. Other options for cats with facial SCC include photodynamic therapy, cryotherapy and intralesional chemotherapy (drugs injected into the cancer site), or a combination of these and radiation. If the ears are affected, a surgical procedure called “total ear canal ablation with bulla osteotomy” provides the best survival times for cats. If the toes are affected by metastasis from the lungs, amputation will not be curative. However, if only one toe is affected and the cat’s lungs are normal on radiograph, it may be prudent to remove that toe.
The prognosis for curing SCC on the nose is excellent if complete surgical resection can be accomplished. The prognosis for curing nasal SCC is also very good even if wide margins are not achieved, if surgery is followed by radiation therapy. Surgical removal of SCC involving the ears also carries an excellent prognosis, if the disease is caught and treated early with a total ear canal ablation and bulla osteotomy. Unfortunately, SCC in cats’ ears can be very aggressive, invading the bones of the skull, in which case the prognosis is poor even with surgery. Metastatic SCC showing up on a cat’s toes also carries a poor prognosis, as amputation will have little effect on the disease. If the digital (toe) carcinoma is primary (has not metastasized from the lungs or elsewhere), then amputation offers a good prognosis, although this form of SCC in cats is very rare.
The only real way to reduce the risk of SCC in cats is to limit their exposure to sun. This is especially important for white and light-colored cats. Waterproof lotion with a high sun protection factor can be applied to at-risk cats.