Page 576 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

554 PART IV Specific Malignancies in the Small Animal Patient

most commonly in the skull (especially oral cavity) and pelvis but More recently, several studies have compared cellular protein
has also been reported in the ribs and vertebrae. The disease in expression in canine and feline OSA to investigate their behav-
ioral disparity. The expression of the cytoskeletal linker proteins
cats differs from that in dogs in that the primary lesions occur
VetBooks.ir more often in pelvic limbs in cats (distal femur and proximal tibia) ezrin and moesin were found to differ between dogs and cats;
In a series of 146 cats
however, the implication of these differences is unclear. Cats more
and it is less metastatic than in dogs.
390
with OSA, 56 cats had extraskeletal OSA; these were most com- commonly expressed the phosphorylated (active) form of ezrin,
monly associated with common injection sites, but other locations but dogs more commonly expressed it in a membranous loca-
included ocular/orbital, oral, intestinal, and mammary sites. 389 tion suggesting greater biologic activity. 404 KIT IHC expression
There is no difference in histopathologic findings for extraskel- was present in 79% of canine OSA but absent in all feline cases.
etal, axial, or appendicular sites. 388 There are also reports of feline Canine KIT mRNA expression was also higher when assessed
extraskeletal OSA in the flank, liver, spleen, kidney, stomach, duo- with RT-PCR. 405 MMP-9 and -2 have also been shown to be
denum, mammary gland, and subcutaneous tissues. 388,391–394 expressed at higher levels in canine OSA compared with feline
OSA generally affects older cats with mean ages of 8.5 to 10.7 OSA, and this may be associated with greater invasive and meta-
years, 387,388,390 but OSA has been reported in cats as young as 5 static behaviors. 406
months and as old as 20 years. 394 The age at presentation for axial
OSA is greater than appendicular OSA. 389 Conflicting reports History and Clinical Signs
on gender predisposition exist with either no difference between
sexes or a slight male predisposition. 387–390 OSA has been reported The most common clinical signs associated with appendicular
to arise after fracture repair in two cats and after RT in another OSA in cats are lameness, swelling, and deformity, depending on
cat. 34,395 OSA has also been diagnosed at a site of prior surgical the location of the lesion. Radiographically, feline OSA appears
resection of a unicameral bone cyst. 396 similar to OSA in dogs with mixed osteoblastic and osteolytic
Osteochondroma and the multicentric form (osteochon- changes and an ill-defined zone of transition between normal
dromatosis or MCE) have both been reported in the cat. 397–399 and neoplastic bone; however, juxtacortical OSA has also been
Osteochondromas are solitary lesions composed of hard, irregular reported in cats. 387 Tumors can reach a large size without evi-
exostoses having a fibrous and cartilaginous cap. 400 Endochon- dence of severe clinical signs. It is rare for cats to have metastasis
dral ossification occurs from the cartilage cap and extends to a at presentation.
variable thickness. This cap tends to blend with adjacent tissue, Cats with virally associated MCE have rapidly progressing, con-
making surgical removal difficult. The lesions in cats differ from spicuous, hard swellings over affected sites causing pain and loss of
dogs because they continue to develop after skeletal maturity and function. Common sites for MCE include the scapula, vertebrae,
in sites not associated with endochondral ossification, such as the and mandible; however, any bone can be affected. Radiographi-
skull. Osteochondromas in cats have a potential for malignant cally, the lesions are either sessile or pedunculated protuberances
transformation and metastasis. from bone surfaces, and the borders between the mass and normal
MCE or osteochondromatosis also occurs after skeletal matu- bone are indistinct. There may be a loss of smooth contour with
rity in cats. In contrast to dogs, the lesions seldom affect long evidence of lysis, particularly if there is malignant transformation.
bones, are rarely symmetric, and are probably of viral rather than
familial origin. There does not appear to be any breed or sex pre- Diagnostic Workup
disposition, although early reports of this condition were in Sia-
mese cats. 401 Affected cats range in age from 1.3 to 8 years (mean Both OSA and MCE may be suspected based on the radiographic
3.2 years). Virtually all cats with MCE are FeLV positive. This appearance of the lesions and the FeLV status of the cat. Defini-
disease has an aggressive natural behavior. tive diagnosis is made by histopathologic evaluation of properly
collected biopsy tissue. Although metastatic rates for cats with
Pathology and Natural Behavior primary bone tumors are low compared with dogs (5%–10%
compared with >90%), three-view thoracic radiographs are rec-
The histologic characteristics of feline OSA are like canine OSA. ommended as part of the clinical staging process. Presurgical eval-
OSA of cats is composed of mesenchymal cells embedded in uation with a complete blood count, serum biochemistry profile,
malignant osteoid. There may be a considerable amount of car- and urinalysis are recommended to rule out concurrent disease.
tilage present, and osteoid may be scant. A feature of some feline
OSA cases is the presence of multinucleate giant cells, which may Therapy and Prognosis
be numerous. Reactive host bone and remnants of host bone are
often present in specimens. Tumors are seen to be invasive; how- Amputation is the recommended treatment for nonmetastatic
ever, some surrounding soft tissue may be compressed rather than appendicular OSA. Complete surgical excision of the primary
infiltrated. There is often variation of the histologic appearance tumor is prognostic for increased ST, DFI, and PFS. 388 Due to
within the tumor with some portions having a more fibrosarco- the low metastatic rate and prolonged MSTs of 24 to 44 months
matous appearance and others more cartilaginous. Feline skeletal with limb amputation alone, 366,368 adjuvant chemotherapy is not
OSA appears similar with respect to grade and histology to canine indicated or recommended in cats. The MST for cats with axial
OSA; however, mitoses are seen almost half as frequently. 388 Some OSA (6.7 months) is lower than either appendicular or extraskel-
authors have described subtypes that resemble those seen in dogs: etal OSA. 389 This most likely reflects the difficulty of achieving
chondroblastic, fibroblastic, and telangiectatic, as well as the giant complete resection and local tumor control in axial sites rather
cell variant. These histologic subtypes, however, do not appear than a difference in their biologic behavior. A combination of sur-
to confer any prognostic predictive value. 402,403 OSAs in cats are gical resection and RT may be appropriate in these cases. SRT
locally aggressive but have a low metastatic rate compared with has been used in several cats with appendicular and axial OSA for
canine OSA. local tumor control.