Page 469 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 23 Cancer of the Gastrointestinal Tract 447

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Undifferentiated Malignancy of Young Dogs excised tumors. In terms of tumor grade, the local recurrence
rate for grade III tumors is 78% and significantly worse than the
recurrence rates of 30% and 47% for grade I and II MLO, respec-
Undifferentiated malignancy is seen in dogs under 2 years of age
VetBooks.ir (range, 6–22 months). 193 Most dogs are large breeds and there is tively. This tumor has a moderate metastatic potential (usually
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to the lung), which is grade dependent, but usually occurs late
no sex predilection. The disease is manifest by a rapidly growing
mass in the area of the hard palate, upper molar teeth, maxilla, in the course of disease. Metastasis is reported in up to 58% of
and/or orbit. 193 Biopsies reveal an undifferentiated malignancy dogs with the median time to metastasis of 426 to 542 days. 27,28
of undetermined histiogenesis. The majority of dogs present with Metastasis is significantly more likely after incomplete surgi-
metastasis to the regional LNs and distant sites. An effective treat- cal resection with a 25% metastatic rate in completely excised
ment has not been identified, although chemotherapy would be tumors and 75% after incomplete resection. Tumor grade also
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necessary considering the high metastatic rate. Most dogs are has a significant effect on metastatic rate with metastasis reported
euthanatized within 30 days of diagnosis because of progressive in 78% of grade III MLO compared with 30% of grade I and
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and uncontrolled tumor growth. 193 60% of grade II tumors. There is no known effective chemo-
Papillary SCC has been reported to occur in the oral cavity of therapy treatment for metastatic disease, but STs greater than
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young dogs (mean age, 3.9 years). The most common location is 12 months have been reported with pulmonary metastasectomy
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the rostral maxilla, and bone invasion is frequently noted on CT. because of the slow-growing nature of this tumor. The overall
Treatment recommendations include complete surgical resection MST is 21 months and is grade dependent, with reported MSTs
or surgical cytoreduction and curettage followed by RT (40 Gy in of 50 months, 22 months, and 11 months for grade I, II, and
20 fractions). In two studies, no dogs developed either local tumor III tumors, respectively. 27,28 Tumor location also has prognostic
recurrence or regional or distant metastasis after treatment with significance because the outcome for dogs with mandibular MLO
either surgery alone or cytoreductive surgery and RT. 74,194 is significantly better, with an MST of 1487 days compared with
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587 days for these tumors at other sites.
Multilobular Osteochondrosarcoma
Odontogenic Tumors
MLO is an infrequently diagnosed bony and cartilaginous tumor
that usually arises from the canine skull, including the mandible, Odontogenic tumors originate from epithelial cells of the dental
maxilla, hard palate, orbit, and calvarium. 27,28 Histologically, lamina. They account for up to 2.4% of all feline oral tumors,
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these tumors are characterized by multiple lobules with a cen- but are rare in dogs. They are broadly classified into two groups
tral cartilaginous or bone matrix surrounded by a thin layer of depending on whether the tumors are able to induce a stromal
spindle cells. 27,28 On imaging, MLO is characterized by a typi- reaction. 195,196 Inductive odontogenic tumors include ameloblas-
cal “popcorn” appearance (Fig. 23.10). Surgery is recommended tic fibroma, feline inductive odontogenic tumor, and complex
for management of the local tumor. The overall rate of local and compound odontomas. 196 Ameloblastomas, AAs, and amy-
recurrence after surgical resection is 47% to 58% and depends loid-producing odontogenic tumors are examples of noninductive
on completeness of surgical resection and histologic grade. 27,28 odontogenic tumors. 195,196 Additional odontogenic tumor groups
The median DFI for completely resected MLO is 1332 days and include tumors composed primarily of odontogenic ectomesen-
significantly better than the 330 days reported for incompletely chyme (cementoma and cementifying fibroma), tumors derived
from the periodontal ligament (peripheral odontogenic fibroma),
cysts of the jaw (dentigerous cyst and radicular cyst), and tumor-
like lesions (giant cell epulis and gingival hyperplasia. 196
Inductive fibroameloblastoma is the most common odonto-
genic tumor in cats, usually occurs in cats less than 18 months of
age, and has a predilection for the region of the upper canine teeth
and maxilla. 5,124,195–197 Radiographically the tumor site shows
variable degrees of bone destruction, production, and expansion
of the mandibular or maxillary bones (Fig. 23.11). Teeth defor-
mity is common. Smaller lesions are treated with surgical deb-
ulking and cryosurgery or premaxillectomy. Larger lesions will
respond to RT. Local treatment needs to be aggressive, but control
rates are good and metastasis has not been reported. 5,124
Odontomas are benign tumors arising from the dental fol-
licle during the early stages of tooth development. 198 Odontomas
induce both enamel and dentin within the tumor. Odontomas
have a biologic behavior similar to ameloblastomas.
Dentigerous cysts are nonneoplastic, circumscribed cystic
lesions originating from islands of odontogenic epithelium. 195
They contain one or more teeth embedded in the cyst wall. Radio-
graphs show a characteristic radiolucent halo surrounding the
nonerupted tooth originating at the cementoenamel junction and
enveloping the crown of the tooth. 199 Odontogenic cysts may rep-
resent an early stage of malignant epithelial tumors. 195 Surgical
• Fig. 23.10 A computed tomography image of a multilobular osteochon-
drosarcoma of the vertical ramus of the mandible. Note the characteristic treatment is recommended, consisting of surgical removal of non-
“popcorn” appearance of the mass. After resection of the vertical ramus, erupted teeth and the cyst lining with possible cancellous bone
this dog was tumor free 3 years after surgery. grafting, to prevent local tumor recurrence. 199