Abstract
Canine glioma is considered a potential model for human glioma, with recent studies of occurrence, therapy, and reclassification supporting the value of the canine model. The current diagnosis of canine glioma is based on morphologic criteria and immunohistochemistry (IHC), including oligodendrocyte transcription factor 2 (Olig2), glial fibrillary acidic protein (GFAP), and 2′, 3′ cyclic nucleotide phosphatase (CNPase). Microtubule-associated protein 2 (MAP2) is a proven marker of human glioma and is used to complement the diagnosis and its specific immunoreactivity pattern contributes to the differentiation of astrocytomas from other glial tumors. The objective of this study was to evaluate whether canine gliomas express MAP2 and to explore differences in the pattern of immunolabeling between different gliomas. Seventy-eight cases of canine glioma were evaluated for MAP2 expression by immunohistochemistry. A glial origin was supported by Olig2 IHC in all cases. MAP2 immunolabeling was evaluated on a semi-quantitative basis, including the percentage of immunolabeled neoplastic cells, as well as the signal intensity, distribution, and pattern of immunolabeling. MAP2 was expressed in all cases, with significant correlation between diagnosis and signal intensity (P = 0.04). MAP2 immunolabeling distribution was dominated by diffuse (34/78; 44%), followed by patchy (20/78; 26%), multifocal to coalescing (16/78; 21%), and scattered (8/78; 10%). All oligodendrogliomas (53/53; 100%) and undefined gliomas (12/12; 100%) revealed a combination of perinuclear and cytoplasmic immunolabeling, and all but 3 astrocytomas had a combination of perinuclear and cytoplasmic processes immunolabeling (10/13; 77%). Significant correlation between immunolabeling pattern and diagnosis was obtained (P = 0.001). The study demonstrates that MAP2 is expressed in canine gliomas and the pattern of expression can also be applied to help distinguish astrocytomas from oligodendrogliomas and undefined gliomas.
Highlights
Canine brain tumors are a potential naturally occurring model for their counterpart human disease and occur at a comparable incidence between the two species [1,2,3,4,5]
The purpose of this study was to evaluate the expression of Microtubule-associated protein 2 (MAP2) in canine gliomas and determine if expression differences exist amongst oligodendroglioma, astrocytoma, and undefined gliomas
Using an online sequence alignment tool, the MAP2 sequences for the dog were compared to sequences for rat and human and sequence homology indicated that an antibody for MAP2 that was derived in a rat would be predicted to label canine tissue
Summary
Canine brain tumors are a potential naturally occurring model for their counterpart human disease and occur at a comparable incidence between the two species [1,2,3,4,5]. Over 50% of gliomas occur in brachycephalic breeds, such as boxers, Boston terriers, and bulldogs. Even among the brachycephalic breeds, boxers, bulldogs, and Boston terriers have a reported higher incidence for astrocytomas in particular [12]. The overall incidence of primary CNS tumors in dogs ranges from 3 to 5% of all neoplasms and is similar to their human counterparts [1, 13]. The prognosis of dogs with primary CNS tumors is guarded to poor, and numerous cases are euthanized after the initial diagnosis. Therapeutic management of these cases, when elected, follows similar protocols as in humans, including surgical resection, radiation, and chemotherapy. Histologic characterization of the neoplasm is integral to deciding on the therapeutic course [14], but therapy is often attempted without fulfilling this step [15]
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