salivary gland TUMORS IN DOGS
Background
Salivary gland tumors are usually seen in older dogs with no obvious gender predilection. Poodles are at higher risk for developing this disease than other breeds.
Carcinomas are the most common tumor type, although salivary glands are occasionally invaded by fibrosarcomas or mast cell tumors.
Enlargement of the salivary gland in a dog is more likely to be an inflammatory process than a tumor.Clinical Parameters
Patients most commonly have a swelling or mass in the neck; however, signs may also include anorexia, dysphagia, and pain on opening the mouth.
Clinical Work-up
The clinical work-up for salivary gland tumors should include a complete blood count, biochemical profile, T4 levels, urinalysis, and cytologic evaluation of the tumor. Local lymph node metastasis may occur; therefore lymph nodes should always have a biopsy or a fine-needle aspiration. Although pulmonary metastases are rare, thoracic radiographs should always be performed as part of a thorough staging scheme. In one study only 8% of the dogs had metastatic disease at time of diagnosis.
The mandibular glands were more likely to be affected than the parotid glands. In many cases, tumor was dispersed throughout the salivary tissue in the submucosa of the oral cavity, tongue, and oropharynx. Surgical excisional biopsy is warranted for localized tumors; however, more diffuse tumors may require incisional biopsy before a definitive procedure.
Therapeutic Approach
Surgical excision in two dogs resulted in local recurrence within 6 months. One of these dogs and two other dogs received 45 Gy of orthovoltage radiation to the surgical site, and none of the three dogs had developed local recurrence or metastasis 12, 25, and 40 months after treatment. Radiation therapy should be considered as an adjunct to surgery for salivary gland tumors. In another group of dogs treated with either surgery, surgery and radiation, or surgery and chemotherapy, the median survival was 550 days. The dogs that were treated with surgery and chemotherapy had shorter survival times than the other two groups. Presumably these dogs had more progressive disease and hence were treated with chemotherapy. In another study six dogs with salivary gland adenocarcinoma were treated with surgery alone, and median survival was 74 days with a range of 42 to 300 days. All of the dogs in this report died of pulmonary metastases.