Page 555 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 25 Tumors of the Skeletal System 533

The reasons for why serum ALP may impart a negative prognosis longer DFI (331 days) than dogs with high survivin immunoreac-
have been incompletely explored; however, two recent investiga- tivity scores within the primary tumor (173 days).
VEGF and the enzymatic activities of COX-2 serve as potent
tions postulate putative mechanisms. In one study of 96 dogs with
VetBooks.ir appendicular OSA, a positive correlation between serum bone ALP regulators of angiogenesis, and their independent expressions
have been associated with poorer prognosis for a variety of
and absolute tumor size was identified; in dogs with progressive
OSA metastatic burden, serum bone ALP increased and coincided cancers. Given that angiogenesis is a necessary step for tumor
with the development of macroscopic metastases. 182 Based upon growth and metastases, both VEGF and COX-2 have been
these findings, the association between increased pretreatment bone investigated in dogs with OSA. 185,187,189 In one study of 25
ALP and negative clinical prognosis may simply be attributed to dogs treated with definitive surgery and systemic chemother-
a greater initial tumor burden and advanced clinical stage of dis- apy, baseline platelet-corrected serum VEGF concentrations
ease. 182 In a second study, increased bone ALP was suggested as an were associated with DFI, but not ST. 187 Dogs with VEGF
epiphenomenon to active endothelin-1 signaling by malignant OSA concentration in the lower 50th percentile achieved a signifi-
cells whereby the secretion of endothelin-1 by OSA cells endowed cantly longer DFI (356 days) than dogs with VEGF levels in
a protumorigenic advantage and secondary “passenger” bone ALP the upper 50th percentile (145 days). In two studies, COX-2
production given the osteoblastic properties of endothelin-1 signal- expression was characterized in primary tumors derived from
96
ing. These two studies suggesting that elevations in bone ALP may 44 dogs and 27 dogs, respectively, with positive COX-2 stain-
be an epiphenomenon of either tumor burden or osteoblastic signal- ing identified in 88% and 93% of tumors evaluated 185,189
ing pathways are consistent with a third study demonstrating that In dogs treated with amputation and doxorubicin (DOX),
canine OSA cell lines derived from dogs with differing bone ALP COX-2 immunoreactivity score, a product of stain intensity
concentrations (normal versus high) do not differ in their in vitro and percentage of positive cells, was potentially correlated with
protumorigenic potentials. 183 disease outcome. Dogs with primary tumors demonstrating
strong stain intensity had a significantly shorter MST (86 days)
Molecular, Genetic, and Immunologic Indices of Prognosis than dogs with tumors staining negative (MST 423 days), poor
The expression of several molecular proteins, including ezrin, (MST 399 days), or moderate (MST 370 days) for COX-2.
recepteur d’origine Nantaise (RON), survivin, vascular endo- Recently, global gene expression analysis of canine OSA stem
thelial growth factor (VEGF), cyclooxygenase-2 (COX-2), and cells identified that COX-2 gene transcription was expressed
heat shock protein (HSP), has been reported to influence DFIs 141-fold greater in canine OSA stem cells compared with non-
and STs in dogs. 98,184–188 Ezrin is a cellular protein belonging stem cells; this suggests that COX-2 activity may play a role in
to the ezrin-radixin-moesin family and serves as a physical and tumor initiation and progression. 190
functional anchor site for cytoskeletal F-actin fibers. Given the HSPs play a critical role in cellular responses to stress and aid in
involvement of ezrin in cytoskeletal remodeling, it has been appropriate protein folding and protection cells after endoplasmic
demonstrated in murine preclinical models that ezrin is neces- reticulum stressors, which otherwise would induce programmed
98
sary for OSA metastases. Through the use of a canine tissue cell death. Cancer cells may deregulate HSP expression to favor
microarray with known clinical outcome data, the presence of survival and HSP gene expression has been investigated in canine
high ezrin staining in primary tumors was associated with a sig- OSA. In a study of dogs with OSA, a significantly increased expres-
nificantly shorter median DFI (116 days) compared with dogs sion of HSP60 was found to be associated with reduced DFIs and
with low primary tumor ezrin staining (188 days). STs in a subset of patients achieving long-term disease control.
Hepatocyte growth factor receptor (MET) and RON are mem- Mechanistic studies demonstrated that knockdown of HSP60
bers of the MET protooncogene family of receptor tyrosine kinases, reduced cell proliferative capacity and induced apoptosis. These
and signaling through MET or RON promotes tumorigenesis and collective findings suggest that HSP60 overexpression might be
the formation of metastases. MET and RON are capable of het- associated with poor prognosis in dogs with OSA. 188
erodimerization with one another, resulting in cellular crosstalk With the near complete sequencing of the canine genome
that may alter the strength and duration of signal transduction and the commercial availability of canine-specific gene microar-
with resultant protumorigenic effects. Given the role of MET and rays, it has become possible to characterize and validate specific
RON in metastases, their expression in OSA has been evaluated in tumor-associated genetic determinants associated with clini-
dogs. 184 Through the use of a canine OSA tissue array with linked cal outcomes and prognosis. In one gene expression profiling
outcome data, expression of RON, but not MET, was prognostic study, primary OSA tissues were analyzed from two groups of
for survival. Dogs with high RON expression in their primary dogs with different clinical outcomes, specifically dogs achieving
tumors had significantly decreased STs than dogs with absent, low, DFIs either less than 100 days or more than 300 days after uni-
or intermediate RON expression. form treatment with amputation and systemic chemotherapy. 106
Survivin is a small protein belonging to the inhibitor of apop- Derived from microarray analysis and confirmed by RT-PCR,
tosis family and participates in the processes of cell division as eight specific gene transcripts were significantly different between
well as apoptosis inhibition. As a dimer, survivin inhibits both poor responders (<100 days) and good responders (>300 days).
caspase-dependent and -independent mediated apoptosis, and its In dogs categorized as poor responders, six transcripts, includ-
expression can promote tumorigenesis. Given the antiapoptotic ing insulin-like growth factor II and alcohol dehydrogenase were
properties of survivin, its overexpression may provide a survival downregulated, and two transcripts were upregulated in com-
advantage to cancer cells and be associated with a negative prog- parison to good responders. To better characterize the molecu-
nosis. In one study, the expression of survivin was characterized in lar pathways associated with the differentially expressed genes
67 primary OSA samples with known outcome data. 186 Survivin identified in microarray analysis, a broader systems approach
expression was detected in 65 tissue samples and expression inten- was used to identify changes in groups of interacting genes or
sity was associated with DFI. Dogs with primary tumors express- pathways that may contribute to metastatic progression or che-
ing low survivin immunoreactivity scores achieved a significantly motherapy resistance. In general, pathway expression differences