At some point during the course of a middle-aged or older cat’s routine physical examination, an attentive veterinarian will carefully study the interior of the patient’s mouth, making sure that the cat’s teeth are intact and that its gums are healthy. The veterinarian will also be looking for any scabby, ulcerating sores, which in most cases can be medically treated and will soon vanish.
In some cases, however, such skin eruptions within the mouth could be a sign that the cat is afflicted with oral squamous cell carcinoma (OSCC). This type of cancer — which accounts for an estimated three-fourths or more of all tumors found in the feline mouth — is extremely lethal. If not recognized at an early stage and successfully treated, OSCC will almost inevitably progress in the soft tissues that comprise the superficial lining of a cat’s mouth and possibly the bony components of the animal’s movable lower jaw (mandible) and fixed upper jaw (maxilla).
Squamous cells — whose name derives from the Latin word for scale — are thin, flat, irregularly shaped cells that constitute the outer layer of the epithelium, the shallow tissue that lines the external and internal surfaces of the organs in a cat’s body. The chief function of this lining is protective — it prevents internal organs and other tissues from rubbing against each other; at the same time, these unique cells facilitate nutrient delivery from one layer of tissue to another. OSCC is considered to be the third most commonly diagnosed type of cancer in cats, accounting for an estimated 10 percent of all feline tumors, exceeded in frequency of occurrence only by lymphoma and skin cancer (which is also largely attributable to the rampant proliferation of squamous cells).
Signs to look for
According to John Berg, DVM, a professor of small animal surgery at Tufts and editor-in-chief of Catnip, the most telling clinical sign of OSCC is “an obvious, visible sore or lump in the mouth.” Other indicators, he points out, include a reluctance to eat, difficulty in swallowing, decline in weight, bad breath, excessive salivation, swelling of the upper or lower jaw, bleeding from the mouth, and the mysterious and sudden loss of an intact tooth. “A lesion that is unrecognized and untreated,” says Dr. Berg, “could potentially progress over a four- to six-month period from a small, innocent-looking, nonpainful tumor that the cat is not even aware of to something that is very difficult to treat.”
Occasionally, the cancer may spread to a cat’s regional lymph nodes, in which case the prognosis will be extremely poor.
Possible risk factors
It is widely believed, although based primarily on preliminary data that have not been scientifically confirmed, that possible risk factors for OSCC include chronic dental disease; the routine ingestion of certain canned cat foods, especially those containing tuna; the use of flea collars; and steady exposure to ambient tobacco smoke.
Regarding canned foods, says Dr. Berg, “There may be carcinogens that are concentrated in the meat or fish. As for flea collars and tobacco smoke, it’s possible that cancer-causing chemicals that they contain collect on a cat’s fur and the animal gets them into its mouth as it grooms itself.”
Older cats are more likely than younger cats to develop OSCC, he notes, but he is unaware of any data showing a predilection for the condition based on breed, gender, or hereditary factors. “As is the case with other types of cancer,” says Dr. Berg, “the prognosis for this particular condition and our ability to treat it is closely associated with how big the lesion is when we first see it. So a cat owner shouldn’t wait until all of the clinical signs appear before having an animal examined by a veterinarian or veterinary dentist. By then, the cancer is often quite advanced.”
The diagnosis of an oral lesion is likely to entail the same measures taken to diagnose any other type of abnormality observed in a cat’s mouth: a thorough medical history and complete physical exam, including bloodwork, urinalysis and perhaps X-rays. But such tests are apt to be inconclusive, says Dr. Berg.
In fact, he notes, blood tests are fairly useless as a means of diagnosing oral cancer, although they can help determine whether the patient has any concurrent disorders and whether an oral cancer has or has not spread to other parts of the body. “The only way in which we can definitively say that it’s squamous cell carcinoma,” he says, “is by means of a biopsy. But many times, we have a very high index of suspicion, as we call it, by just looking at the lesion.”
Treatment options for OSCC are limited, Dr. Berg points out, especially if the cancer has reached an advanced stage. “Most oral tumors,” he notes, “are locally invasive. They tend to stay in the mouth and not metastasize. They don’t seem to be very responsive to chemotherapy.” As for radiation therapy, he says: “The results have been mixed. In general, these tumors are not considered to be particularly radiation-responsive, although it is now believed that certain drugs called radiation sensitizers, which are given along with the radiation, can improve the prognosis. So there is some evidence starting to accumulate that radiation might play a larger role in the treatment of these tumors in the future.”
Surgery is most common
Given the limited efficacy of chemotherapy and radiation therapy in these cases, surgical removal of a tumor is the most frequently chosen treatment option for OSCC, according to Dr. Berg. “The first question we ask ourselves,” he says, “is ‘Can this growth be surgically removed?’ The problem with this disease in cats is that the tumor is highly invasive — it spreads deeply into soft tissues and invades underlying bone very easily, and a cat’s mouth is a relatively small space. So it doesn’t take a whole lot of invasion to create a major surgical challenge. If we don’t spot the problem early, it may be beyond what we can treat surgically. But when we do spot the cancer at an early stage, it often can be treated. The challenge with surgery is to get the whole tumor out — and the classic tumor tends to grow beyond what we can see.” (A CT scan will in most cases be required to assess whether a tumor is indeed amenable to surgery.)
Whether the surgery involves the lower jaw (called a partial mandibulectomy) or the upper portion of the oral cavity (a maxillectomy), the objective will be to remove not only the visible tumor but also the area of tissue that immediately surrounds the growth. “Either of these procedures,” says Dr. Berg, “will require the removal of some teeth and the bone that surrounds them. The objective is to remove a complete margin of tissue around the tumor so that it cannot grow back.”
Cats don’t tolerate this surgery very well in the short run, he notes, and they tend to avoid eating following the operation. Consequently, he explains: “On the same day that the surgery is done, we place a feeding tube through the skin on the side of the neck and into the esophagus, and we leave it there until the cat shows a desire to eat orally again, which could take as long as three or four weeks. Cats tolerate these esophageal tubes — or ‘e-tubes’ — extremely well (see photo on page 14). And once the cat begins to eat well on its own again, we just slip the tube out and the cat will do very well after that.”
The median survival time of cats that have successfully undergone such surgery, says Dr. Berg, is on the order of a year and a half. “But if we don’t remove all of the tumor,” he notes, “it is highly likely to grow back in a matter of a few months, and recurrent tumors are always much harder to remove than initial growths.”
Reducing the risk
Owners may reduce the chances that a cat will develop OSCC by limiting their exposure to ambient tobacco smoke and avoiding flea collars. They should also get in the habit of routinely examining a cat’s face and oral cavity for any suspicious skin eruptions that might indicate the presence of a cancerous growth.
But — above all — because OSCC is a rapidly progressing and particularly lethal disorder, Dr. Berg urges owners of cats that are seven years of age and older to have their cats undergo thorough dental and oral examinations by a veterinarian every six months.