Salivary Gland Tumor Diagnosis
Salivary gland tumors in dogs and cats are uncommon. Affected animals are older (> 10 years), there is no breed or sex predilection, and the cause is unknown. This case report describes mandibular salivary gland adenocarcinoma in a dog. A 9-year-old female presented with a firm, painless swelling, 3 cm in diameter, at the base of the left ear. The mass was firmly attached to deeper tissues, and lymph nodes were normal. Fine-needle aspiration biopsy showed an epithelial tumor. Based on cytologic appearance, a presumptive diagnosis of salivary gland carcinoma was made. Skull/cervical and thoracic radiographs were taken to rule out metastasis. The mass was then surgically removed, and biopsy confirmed the cytologic diagnosis of salivary gland adenocarcinoma.
In discussion of the case, the authors note that tumor cells from salivary gland adenocarcinomas may show a wide variety of patterns on cytologic examination. Histologic evaluation of the tumor is necessary to confirm histotype and growth pattern of the neoplasm. Adenocarcinomas, such as the one described here, have a variety of glandular patterns with cytologic features of cancer and infiltrative borders. Thus, tumors may recur locally if excision is incomplete. During initial investigation, fine-needle aspiration biopsy can be helpful to distinguish salivary gland tumors from other salivary lesions and to help choose appropriate surgical treatment, which should be more radical when cytologic evaluation suggests carcinoma.
COMMENTARY: This case report emphasizes both the power and limitations of presurgical fine-needle aspiration. Cytologic features may help to differentiate inflammatory lesions from neoplastic ones, and such features as pleomorphism, prominent nucleoli, anisocytosis, and anisokaryosis (as described in this case) indicate that the lesion is probably malignant. Cytologic diagnosis of the exact type of cancer is rarely possible, and rarely necessary, as biopsy (excisional or incisional) is needed to assess lymphatic or vessel invasion (seen on biopsy in this case) and tumor grade. None of these can be assessed through cytologic evaluation but are extremely important for prognosis and treatment decisions. Cytologic evaluation assists the veterinarian in offering appropriate further diagnostics, rather than a "2-week trial of antibiotics," which could delay appropriate diagnosis and treatment; cytologic diagnosis does not, however, replace histopathologic evaluation for a cancer patient.
Case report: Cytological diagnosis of mandibular salivary gland adenocarcinoma in a dog. Militerno G, Bazzo R, Marcato PS. J VET MED 52:514-516, 2005.