Salivary Gland Tumors in Cats

Quick Facts at a Glance:

• Mass noticed by owner is the most common presenting complaint
• Mandibular salivary glands are most often affected
• Siamese cats may be predisposed
• Males are more often affected than females
• Simple adenocarcinoma is the most common histologic (biopsy) diagnosis
• Median survival time is 516 days following surgery

Who gets salivary gland tumors and what are the presenting signs?

Salivary gland tumors are rather uncommon with an overall incidence of

0.17%. These tumors are primarily found in older cats with a median age at presentation of 12 years (range7-22 years). Males are more commonly affected than females. Siamese and Siamese mix breeds represent almost 1/3 of the population of cats reported with this disease.

The most common reason for presentation is the finding of a mass by the pet owner, in the region of the mandibular (neck area) salivary gland. Other presenting symptoms include halitosis (bad breath), weight loss, loss of appetite, Horner's Syndrome and exopthalmus (unusual protrusion of the eye). Occasionally, dysphagia (difficulty swallowing), sneezing and voice changes are noted.

What diagnostic tests should be performed?

As with any older cat with a diagnosis of cancer, a general health evaluation including a complete blood count (cbc), platelet count, biochemical profile, T4 level, urinalysis and viral status should be done. Because of the high rate of metastasis (spread) associated with salivary gland tumors, chest x-rays and abdominal ultrasound are important prior to establishing a treatment plan. MRI or CT scan of the cervical (neck) region allows for delineation of the tumor and identification of enlarged lymph nodes that might not be palpable (able to feel). These tests are particularly helpful for planning for radiation therapy.

How does stage of disease affect prognosis?

Cats often have very advanced disease at the time of diagnosis. In one study, 39% of cats had regional lymph node metastasis and 16% had pulmonary metastasis (spread to the lungs) at the time of presentation. The average survival time of cats with salivary gland carcinoma of all stages and histologic diagnoses is 516 days following surgery (with or without radiation or chemotherapy). To date, stage of disease has not been correlated with survival time in cats. Interestingly, mitotic index has been inversely related to survival time. Cats with tumors with a low mitotic index (less than 10 cells per high-powered microscopic field) have statistically shorter survival time (average 225 days) as compared with cats with tumors with a high mitotic index (average 1500 days). No other histopathologic feature appears to correlate with prognosis.

What is the treatment of choice?

Surgical resection (removal) of the salivary gland tumor is the preferred treatment. Due to the advanced stage of disease at presentation and location of the mass, complete surgical resection is not often feasible. Time to recurrence (re-growth) is variable. Radiation therapy is recommended after surgery to delay tumor recurrence. It is not clear how beneficial radiation therapy is in this setting. Relatively small populations of patients with salivary gland carcinoma treated with a combination of surgery and radiation have been compared to patients treated with surgery only, preventing valid statistical comparison of results. Due to the high metastatic rate of salivary gland carcinoma in cats, chemotherapy is recommended as an adjuvant (additional) therapy to surgery alone or to combination therapy (surgery and radiation). Unfortunately, a concensus does not exist in veterinary medicine regarding which drugs or drug combinations are most beneficial. Chemotherapy drugs that are commonly used in this setting include carboplatin, doxorubicin, cyclophosphamide and more recently, gemcitabine.

What therapies are on the horizon?

Surgery, radiation therapy and chemotherapy will always remain important components of treatment of this disease. Because local recurrence is a major concern, therapies directed at inhibiting angiogenesis (blood vessel growth) will likely have significant impact on overall survival times in these patients.

What is the ultimate progression of this disease?

While survival times can exceed 3 years in some patients, local disease ultimately becomes impossible to control. The invasive nature of this tumor causes cervical (neck) pain, loss of appetite and weight loss leading to the rapid decline in the patient's quality of life.