Page 462 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

440 PART IV Specific Malignancies in the Small Animal Patient

but can include permanent alopecia, skin fibrosis, bone necrosis
and oronasal fistula formation, development of a second malig-
nancy within the radiation field, keratoconjunctivitis sicca,
VetBooks.ir cataract formation, xerostomia, and retinal atrophy. 43,130–132
Orthovoltage radiation may be associated with a higher inci-
dence of second malignancies and bone necrosis than megavoltage
irradiation. 32,130,131

Chemotherapy
The major problem with most oral tumors is control of local dis-
ease; however, chemotherapy may be indicated for some tumors
with higher metastatic potential, especially oral MM in dogs, 9,30–
68 tonsillar SCC in cats and dogs, OSA in dogs, 122 and possibly
oral SCC in cats. 89–112
Prognosis
• Fig. 23.7 Rim resection of an acanthomatous ameloblastoma in a dog.
The rim resection has been performed with a 24-mm biradial saw to pre- Clinical series of more than 750 dogs with various oral malignan-
serve the ventral cortex of the mandibular body and hence prevent post- cies treated with either mandibulectomy or maxillectomy have been
operative mandibular drift.
described. 13–24,161–164 The majority of cases were treated with sur-
gery alone. Unfortunately, the methods of reporting and outcome
results vary with each paper. Overall, the lowest rates of local tumor
recurrence and best survival times (STs) are reported in dogs with
AA and SCC, whereas FSA and MM are associated with the least
favorable results. 13–24 Most of these reports suggest that histologi-
cally complete resection, smaller diameter, and a rostral location are
favorable prognostic factors. In two studies of 142 dogs treated
24
with either mandibulectomy or maxillectomy, tumor-related deaths
were 10 to 21 times more likely with malignant tumors, up to five
times more likely with tumors located caudal to the canine teeth,
and two to four times more likely after incomplete resection. 22,23
Rostral locations are usually detected at an earlier stage and are
more likely to be resectable with complete surgical margins. Local
tumor recurrence is more frequent after incomplete resection with
15% to 22% and 62% to 65% of tumors recurring after complete
and incomplete excision, respectively. 22,23 Recurrent disease nega-
tively affects ST because further treatment is more difficult and
31
the response to treatment is poorer. FSA continues to have high
local recurrence rates in most studies, and more aggressive surgical
approaches or adjuvant therapies, such as postoperative RT, should
be considered. 24,115 On the other hand, MM is controlled locally in
75% of cases, but metastatic disease requires more effective systemic
adjuvant therapy.
• Fig. 23.8 The typical appearance of a dog 6 months postoperatively
after subtotal unilateral mandibulectomy for an osteosarcoma. The tongue Malignant Melanoma
will often hang out and the remaining hemimandible will drift toward the The prognosis for dogs with oral MM is guarded. Metastatic dis-
resected side.
ease is the most common cause of death, with metastasis to the
lungs reported in 14% to 67% of dogs. 9,13–24, 30–68 Surgery or

and some benign tumors, such as AA, 130–132 are known to be RT can provide good local control, but the majority of dogs will
radiation responsive, and RT should be considered in the primary fail treatment because of metastatic disease and hence the search
treatment of these tumors. RT can also be used for the palliation for effective adjuvant immunotherapy holds the most promise to
of oral SCC in cats and a variety of hypofractionated, accelerated, ultimately improve outcomes.
and stereotactic RT protocols have been described. 96–106 Surgery is the most common treatment for management of
Acute effects are common but self-limiting. These include alo- the local tumor. The median survival time (MST) for untreated
pecia and moist desquamation, oral mucositis, dysphagia, and dogs with oral MM is 65 days, whereas tumor control and STs
31
ocular changes, such as blepharitis, conjunctivitis, keratitis, and are significantly better when surgery is included in the treatment
32
uveitis. 43,80,81,116,117,130 The acute effects of coarse fractionation plan. The overall local tumor recurrence rate after surgery is up
are less than experienced with the full-course protocols used for to 45%, 24,40,41 with local tumor recurrence rates of 22% after
oral SCC and dental tumors and usually resolve rapidly. 44–49,96–104 mandibulectomy and 48% after maxillectomy. 7,18,19 The median
Late complications are rare, occurring in fewer than 5% of cases, ST (MST) for dogs with MM treated with surgery alone varies