Page 1317 - Clinical Small Animal Internal Medicine

137 Cancer of the Nose and Mouth 1255

consisting of 2.7–4.2 Gy per fraction with a total dose Prognosis
VetBooks.ir ranging from 48 Gy to 57 Gy. More recently, stereotactic Malignant Melanoma
radiation is being used as treatment of non-resectable
The prognosis for dogs with oral malignant melanoma is
oral tumors. Protocols typically consist of 1-3 high doses
of radiation precisely targeted at the tumor, with rapid guarded. In one study, median survival time (MST) of
dogs with untreated oral melanomas was two months.
dose fall off outside of the tumor. These protocols are Aggressive resection by mandibulectomy or maxillec-
proving to provide durable control of disease, with tomy can be effective for control of these tumors but
decreased acute side effects when compared to tradi- postsurgical recurrence has been reported to develop in
tional radiation protocols; however published studies are 8–85% of dogs and metastasis to regional lymph nodes,
still limited. lungs, or other viscera may develop in as many as 95%.
When using radiation therapy alone, tumor control is
better achieved with smaller lesions (T1 or T2 tumors). Metastasis, particularly to the lungs, is the most com-
mon cause of death, being reported in 15–67% of dogs.
With megavoltage radiation, local recurrence is reported Median survival times for dogs with OMM treated with
in up to 30% of cases. When compared to T1 tumors, surgery are approximately 17–18 months, 5–6 months,
tumor progression is three times more likely with T2 and three months with stage I, II, and III disease,
tumors and 5–8 times more likely with T3 tumors. Local respectively.
tumor control and survival time, however, can be Coarse fraction radiation treatment effectively
improved by combining surgery and radiation therapy. achieves local control in dogs with melanomas.
Acute radiation side‐effects are common during treat-
ment of oral tumors, but these are generally self‐limiting. Reduction in tumor size is attained in 83–100% of dogs,
and a complete response rate has been reported to be as
They can include alopecia and moist desquamation, oral high as 70%. In a retrospective study of 140 dogs with
mucositis, dysphagia and ocular changes such as blephar- OMM treated with radiation therapy, it was found that
itis, conjunctivitis, keratitis, and uveitis. Late side‐effects systemic chemotherapy had no impact on the develop-
are rare (<5%), but are much more serious as they are ment of metastatic disease, time to first event, or sur-
permanent. Late side‐effects include skin fibrosis, bone vival. In the same study, tumor location, bone lysis, and
necrosis and oronasal fistula formation, development of tumor volume were all variables identified to predict
a second malignancy within the radiation field, kerato- time to first event and survival. If none of these risks
conjunctivitis sicca, cataract formation, and ocular were present, median survival for dogs with malignant
atrophy.
melanomas treated with radiation therapy was 21
months, and if one, two, or three risk variables were pre-
Chemotherapy sent, median survival time was 11 months, five months,
Frontline treatment for most oral tumors is control of or three months, respectively.
local disease with surgery and/or radiation therapy. The use of immunotherapy for malignant melanoma is
Chemotherapy is indicated for some tumors due to their showing some promise, but most results involve small
high metastatic potential. OMM and tonsillar SCC are numbers of dogs in phase I trials. Xenogeneic vaccine
both highly metastatic tumors, but unfortunately their studies for dogs with stage I–III OMM report median
response to chemotherapy is low. survival times of almost three years when local regional
The nonsteroidal antiinflammatory drug piroxicam, a
COX‐2 inhibitor, has been shown to have some effect control had been achieved and patients received vaccine
versus 1.5 years when patients were given the same
against canine oral SCC. Expression of COX‐2 has also vaccine, but failed locally.
been noted in feline oral SCC, but no improvement has
been seen in the management of these tumors when
piroxicam has been used. Canine Squamous Cell Carcinoma
Following mandibulectomy for canine nontonsillar SCC,
Immunotherapy the median survival ranges from 19 to 26 months versus
A DNA vaccine against tyrosinase is now commercially 10–19 months following a maxillectomy. Tonsillar SCC
available for the adjunctive treatment of dogs with carries a graver prognosis. Due to higher local recur-
OMM. To maximize chances of long‐term survival, it rence and metastatic rates, studies report one‐year
has been found that the vaccine is most effective when survival times of only 10%.
residual disease is minimized and local regional control Full‐course radiation therapy, either alone or as an
has been achieved. Adverse reactions following adminis- adjunct following incomplete surgical resection, is also a
tration of the vaccine have been found to be minimal, successful treatment modality for the management of
with the most notable side‐effects consisting of bruising oral SCC in dogs. With full‐course radiation, a study of
and hematoma formation. 39 dogs reported an overall median progression‐free