Veterinary Society of
Surgical Oncology

GENERAL CONSIDERATIONS

Epidemiology

  • oral tumors account for 3%-10% of feline tumors and > 90% malignant
  • oral tumors account for 6% of canine tumors and is the 4th most common canine cancer
  • relative risk of oral tumors is 2.4-times greater in male dogs
  • oral tumors commonly arise from gingiva or tongue in cats and the gingiva in dogs, but they can arise from buccal mucosa, mandible, maxilla, palate, dental structures, and tonsils

Histologic Types of Oral Tumors

General Considerations

  • SCC and FSA are the most common oral tumors in cats
  • SCC, FSA, and malignant melanoma are the most common oral tumors in dogs

Oropharyngeal Tumors

  • epithelial oral tumors include SCC, papilloma (dogs), fibropapilloma, and others such as intraosseous carcinoma and invasive nasal carcinoma
  • melanocytic oral tumors include malignant melanoma
  • mesenchymal oral tumors include fibroma and FSA, OSA, HSA, granular cell tumor (or myoblastoma), mixed mesenchymal sarcoma, and others such as neurofibrosarcoma, anaplastic sarcoma, myxosarcoma, CSA, and rhabdomyosarcoma (rare)
  • round cell oral tumors include MCT, LSA, and transmissible venereal tumor

From: Withrow SJ & MacEwen EG (eds): Small Animal Clinical Oncology (3rd ed).

Odontogenic Tumors

  • periodontal odontogenic tumors include acanthomatous epulis, ossifying epulis, fibromatous, and giant cell epulis
  • epithelial odontogenic tumors include ameloblastoma, keratinizing ameloblastoma (cats), ameloblastic adenomatoid, calcifying epithelial odontogenic tumor, dentinoma, odontoma, and inductive fibroameloblastoma (cats)
  • mesenchymal odontogenic tumors include fibromyxoma, cementoma, and odontogenic fibroma

CLINICAL FEATURES

Signalment

  • oral tumors usually occur in older animals, however, exceptions include FSA in large dogs, papillary SCC (< 6 months), undifferentiated sarcoma (< 2 years), and viral-induced papillomatosis (< 1 year)
  • malignant melanoma and FSA are more common in male dogs
  • breed predisposition: Cocker Spaniel, Weimaraner, GSD, GSHP, Golden Retriever, and Boxer
  • Dachshund and Beagle have a low risk of developing oral tumors
  • small breeds have higher incidence of malignant melanoma and tonsillar carcinoma
  • dogs with heavily pigmented oral mucosa are predisposed to malignant melanoma

Clinical Signs

  • oral tumors can be either proliferative or ulcerative
  • clinical signs in cats include facial asymmetry, ptyalism, anorexia, sneezing, nasal discharge, pawing at mouth, changed eating habits, oral hypersensitivity, loose teeth, dysphagia, weight loss, and halitosis
  • clinical signs in dogs include decreased appetite, halitosis, tooth loss, bloody salivation, exophthalmos, epistaxis, dysphagia, difficult and painful mastication, and psychogenic polydipsia
  • loose teeth with otherwise normal dentition is suggestive of bone lysis secondary to neoplasia, especially in cats
  • facial deformity occurs only if the disease is advanced
  • dyspnea is common with large tonsillar tumors, caudal pharyngeal tumors, and metastatic lymphadenopathy
  • regional lymph nodes (i.e., mandibular and retropharyngeal) palpated for enlargement and asymmetry
  • regional lymph node FNA if palpable or abnormal
  • metastasis in 17% of oral tumors especially malignant melanoma, MCT, and tonsillar SCC

DIAGNOSIS

Biopsy

  • biopsy is required for diagnosis and differentiation of inflammatory and neoplastic tissue
  • intraoral biopsy should be performed to avoid tumor seeding in skin and increasing surgical margins
  • biopsy is possible in conscious animals if the mass is ulcerated or exophytic
  • large incisional biopsy is indicated as oral tumors are often infected, inflamed, and necrotic
  • electrocautery may distort tumor architecture and should only be used for hemostasis after biopsy collection
  • biopsy should be located at the edge and centre of lesion to increase diagnostic yield
  • biopsy site should be planned to minimize contamination of normal tissue
  • cytologic preparation is usually unrewarding because of necrosis and inflammation

Imaging

  • oral survey radiographs determine clinical stage and extent of surgical margins
  • intraoral (preferred), open-mouth, oblique lateral, dorsoventral, and ventrodorsal survey radiographs to determine extent of bone lysis, although occasionally bony reaction is proliferative (i.e., OSA)
  • radiographs underestimate the extent of bone destruction as lysis is only observed with > 30% cortical bone loss
  • fixation of tumor to bone suggests minimum microscopic invasion of bone
  • CT and MRI may be more valuable than survey radiographs for local and distant tumor extent
  • 3-view thoracic radiographs performed before surgical biopsy
  • pulmonary metastatic disease is most common for malignant melanoma and SCC of the caudal oropharynx

From: Withrow SJ & MacEwen EG (eds): Small Animal Clinical Oncology (3rd ed).

Clinical Staging

  • clinical staging is based on size, regional lymph node involvement, and distant metastasis
  • FNA or excisional biopsy of regional lymph nodes is performed if the lymph node is enlarged, fixed, or painful
  • false-negative FNA aspirates are possible due to small sample size and random distribution of tumor cells
  • majority of dogs have stage III or IV disease at diagnosis

TREATMENT

General Considerations

  • aggressive local therapy is indicated if no pulmonary involvement: surgery, radiation therapy, or cryosurgery

Surgical Therapy

  • mandibulectomy and maxillectomy are usually well tolerated and indicated for malignant tumors and bony invasion
  • surgery is usually the most economical, fast, and curative treatment
  • minimum margins of 2 cm and more for feline SCC due to high local recurrence rate
  • increased survival time
  • morbidity greater with more extensive surgery
  • owner satisfaction with cosmetic and functional outcome > 85%
  • problems: wound dehiscence, tumor recurrence, and metastatic disease
  • surgical approach can include access to ipsilateral parotid, mandibular, and medial retropharyngeal lymph nodes

Cryosurgery

  • indicated for lesions < 2 cm in diameter, fixed, and minimally invasive into bone
  • cryosurgery of larger lesions associated with iatrogenic fracture (mandible) or oronasal fistula (maxilla)
  • soft tissue cancers or larger cancers should be managed surgically

Hyperthermia

  • no advantage compared to surgery or cryosurgery alone
  • bone penetration is less than cryosurgery and hyperthermia is less reliable
  • hyperthermia can be used in conjunction with radiation therapy

Radiation Therapy

  • indications for radiation therapy include:
  • radiosensitive tumors: acanthomatous epulis, SCC ± malignant melanoma
  • inoperable tumor of any histologic type (palliative)
  • incomplete resection with microscopic disease
  • success of radiation therapy depends on histologic type and clinical stage:
  • median DFI 36 months for SCC, 26 months for FSA, and 8 months for malignant melanoma
  • local tumor recurrence occurs within the radiation field suggesting a higher dose may be required

Chemotherapy

  • palliative for malignant melanoma, high histologic grade tumors, and advanced metastatic disease

ORAL TUMORS

T0

No evidence of neoplasia

Tis

Carcinoma in situ

Primary Tumor

T1

Tumor diameter < 2 cm (T 1a no bony invasion and T 1b bony invasion)

T2

Tumor diameter 2-4 cm (T 2a no bony invasion and T 2b bony invasion)

N0

No evidence of regional lymph node involvement

N1

Movable ipsilateral regional lymph node (N 1a no tumor cells and N 1b tumor cells)

Node

M0

No evidence of metastasis

M1

Evidence of distant metastasis with site specified

Metastasis

T3

Tumor diameter > 4 cm (T 3a no bony invasion and T 3b bony invasion)

N2

Movable contralateral or bilateral regional lymph node (N 2a no tumor cells and N 2b tumor cells)

N3

Fixed regional lymph node

Clinical Stage

I

II

III

T

T1

T2

T3

T1-3

N

N0-2a

N0-2a

N0-2a

N1b

M

M0

M0

M1

M0

IV

T1-3

T1-3

N2b-3

N0-3

M0

M1

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