Page 470 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

448 PART IV Specific Malignancies in the Small Animal Patient

SECTION B: SALIVARY GLAND NEOPLASIA
VetBooks.ir SARAH E. BOSTON

Incidence and Risk Factors

Salivary gland neoplasia in dogs and cats is rare; however, it is a
significant cause of salivary disease. In a study of the histopatho-
logic diagnosis of salivary gland biopsies in dogs and cats, 30%
were diagnosed with neoplasia. 203 The second most common
diagnosis in that study was sialadenitis (26%).

Pathology

Salivary gland neoplasms are primarily malignant epithelial tumors.
Simple adenocarcinoma is the most common histopathologic diag-
nosis, with other types of carcinomas being represented second
most commonly. 204 Other reported tumors in this location include
oncocytoma 205 and carcinosarcoma in cats 206 ; and pleomorphic
adenoma, 207 myoepithelioma, 208 OSA, 209 and mast cell tumor in
• Fig. 23.11 An intraoral radiograph of the rostral mandible in a dog with dogs 210 ; however, these are single case reports and are rare.
an ameloblastoma. Note the expansile mandibular mass. The tumor was
curetted and filled with cancellous bone graft and the dog was tumor free History and Clinical Signs
1 year after surgery.
Clinical signs of salivary neoplasia and sialadenitis may be simi-
Osteomas lar. The most common presenting complaint in a retrospective of
salivary gland neoplasia in dogs and cats was the presence of a
Osteomas have been described in both dogs and cats. 200,201 mass. 204 Other presenting complaints included halitosis, weight
Osteomas are benign tumors of histologically normal mature loss, anorexia, dysphagia, exophthalmos, Horner’s syndrome,
compact and/or trabecular bone. 201 They are slow growing and sneezing, and dysphonia. 204 In one retrospective study of dogs and
rarely cause clinical signs unless the mass interferes with adja- cats, there appeared to be a predilection for male sex and Siamese
cent structures or prevents occlusion. 200,201 Radiographically, breed in cats. 204 In that study, the mandibular salivary gland was
osteomas are typically proliferative masses with no evidence most commonly affected in cats and the parotid salivary gland was
of bone lysis. 200,201 They are classified as peripheral, central, most commonly affected in dogs. 204
or extraskeletal in people, and peripheral and central osteomas
have been described in dogs. 200,201 Surgical excision is usually Diagnostic Techniques and Workup
curative. 200,201
An FNA for cytology should be performed as a first step in attempt-
Comparative Aspects 202 ing to distinguish between benign and malignant disease. 211 If this
is not successful, a needle-core, incisional, or possibly an excisional
SCC accounts for the vast majority of oral cancer in humans. Oral biopsy can be considered for histopathology. Salivary gland adeno-
tumors are associated with alcohol and tobacco use and usually carcinoma is both locally aggressive and has metastatic potential, and
occur in patients more than 40 years old. Patients with oral cancer hence local and distant staging should be considered before defini-
have an increased risk of developing esophageal and lung cancer. tive treatment. Thoracic radiographs or CT can be performed to
Tumors are staged similar to animals and clinical stage influences assess the lungs for metastatic disease. An ultrasound of the affected
both treatment options and prognosis. area can also be performed for initial staging and possibly to obtain
Surgery and RT are the only options that provide the oppor- an ultrasound-guided aspirate of the mass and/or regional LNs. 212
tunity for a cure. Surgery and radiation are occasionally com- The medial retropharyngeal LNs are the primary lymphatic drain-
bined, especially because neither modality is likely to achieve age center of the salivary glands and should be evaluated cytologi-
a cure rate greater than 70% when used as sole therapy. Che- cally and/or biopsied for histopathology. 213 Ultimately, a CT scan
motherapy has a limited role for control of local disease but of the head and thorax is recommended for staging and surgical
has shown promise, often in combination with radiation, for planning. 212 In cases where surgery may not be possible, the patient
advanced stage cancer. should be positioned for a concurrent radiation planning CT for
Prognosis is strongly correlated to histologic grade, stage, potential RT alone. In one retrospective study, cats presented at a
and site. Metastasis, particularly to the regional LNs, is more more advanced stage of disease than dogs, suggesting that this dis-
frequent with tonsillar and pharyngeal SCC and larger sized ease may be more aggressive in cats. 204
tumors. Tumors of the pharynx and caudal tongue are associated
with a worse prognosis than cancers of the rostral tongue and Therapy
oral cavity because of the higher incidence of nodal metastasis
and difficulty in controlling disease once it has spread beyond Surgery is the mainstay of therapy. Using a CT scan for surgical
the primary site. planning, the affected salivary gland is removed. By definition,