+ Biologic Behavior
- Rare with an overall incidence of 0.17%
- However, salivary gland neoplasia comprises 30% of all salivary gland pathology
- Majority of salivary gland tumors are malignant and epithelial (84%) with ADC most common
- Other salivary gland tumors include mucoepidermoid carcinoma, complex carcinoma, cystadenocarcinoma, acinic cell carcinoma, undifferentiated carcinoma, SCC, OSA, FSA, giant cell tumor, MCT, and LSA
- Major (i.e., parotid, mandibular, sublingual, and zygomatic) and minor accessory salivary glands can involved
- Metastasis to the regional lymph node in 39% and distant sites in 16% cats
- Metastasis to the regional lymph node in 17% and distant sites in 8% dogs
- Benign salivary gland tumors are rare (compared to humans) although benign lipomatous infiltration, calcinosis circumscripta, and adenoma have been reported
CLINICAL FEATURES
+ Signalment
- Age: older (> 10-12 years)
- Breed predisposition: Siamese cats and Spaniel breeds
- Sex predisposition: males in cats with a male-to-female ratio of 2:1, but no sex predilection in dogs
+ Clinical Signs
- Clinical signs are non-specific and include halitosis, dysphagia, and exophthalmos
- Unilateral firm, painless swelling of the:
- Upper neck with mandibular and sublingual salivary gland tumors
- Ear base with parotid salivary gland tumors
- Upper lip or maxilla with zygomatic salivary gland tumors
- Mucous membrane of lip or sublingual area with accessory salivary gland tumors
- DDx: mucocele, abscess, salivary gland infarction, sialadenitis, LSA, or reactive lymphadenopathy
DIAGNOSIS
+ General Considerations
- FNA to differentiate non-neoplastic from neoplastic masses
- Regional radiographs to identify periosteal reaction or displacement of adjacent structures
- Incisional biopsy for definitive diagnosis
+ Clinical Staging
TREATMENT
+ Surgical Treatment
- Surgery is recommended if possible but many lesions are extracapsular, invasive, and involve vital structures
- Parotid gland resection is difficult due to poorly defined margins and facial nerve involvement
- Complete extirpation of the ipsilateral neck can be performed with good functional outcome despite poor ability to blink and predisposition to KCS (treatment: tarsorrhaphy and eye drops)
- Surgery and radiation therapy has been used to treat 3 cases with microscopic disease resulting in good local control and prolonged survival
- Role of chemotherapy unknown
+ Prognosis
- MST 516 days in cats
- MST 550 days in dogs
- Surgery and radiation therapy can provide permanent local control and long-term survival
- Incomplete resection will result in local recurrence
- Histologic grade is not prognostic for salivary gland ADC
- Poor prognostic factors in cats: low mitotic index (≤ 10 v > 10)
- Poor prognostic factors in dogs: stage III-IV disease v stage I-II disease
SALIVARY GLAND TUMORS
| T0 | No evidence of neoplasia | T1 | Tumor < 2 cm in diameter - Primary Tumor | T2 | Tumor 2-4 cm in diameter |
| T3 | Tumor > 4 cm in diameter | N0 | No evidence of lymph node involvement |
| N1 | Regional lymph node involvement - Node |
| M0 | No evidence of metastasis |
| M1 | Evidence of distant metastasis with site specified - Metastasis |
Clinical Stage
| I | II | III | T | T1 | T2 | T3 | N | N0 | N0 | N0 | M | M0 | M0 | M0 | IV | T1-3 | N1 | M0 | V | T1-3 | N0-1 | M1 |
| Salivary Gland | Mandibular | Parotid | Sublingual and Minor Salivary Glands | Zygomatic | Undetermined Salivary Glands | Cat | 59% | 19% | 6% | 3% | 13% | Dog | 30% | 50% | 12% | 4% | 4% |