Page 684 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

662 PART IV Specific Malignancies in the Small Animal Patient

that seen in humans, with oligodendrogliomas accounting for a Palliative Care
significantly higher proportion of all canine gliomas. 1,2,64 Insuf- The primary palliative therapies administered to brain tumor
patients are anticonvulsant drugs (ACD) for tumor-associated
ficient data currently exist in veterinary medicine to evaluate the
VetBooks.ir effect of glioma grade on clinical outcome. Intracranial gliomas structural epilepsy, corticosteroids targeting peritumoral vasogenic
5
edema, and analgesics for signs consistent with somatic, visceral,
are rare in cats, and oligodendrogliomas are the most common
type observed. 3,65,66 or neuropathic cancer pain. 7,9,30 Although seizures are one of the
In the dog, approximately 40% of CPTs are grade I CPP, 60% most common clinical signs associated with brain tumors, ideal
are grade III CPC, and nearly 50% of CPTs occur in the fourth ACD protocols for the treatment of tumor-associated epilepsy
21
ventricular region. Atypical (grade II) choroid plexus papillomas are currently unknown. 2,24,27,28 Phenobarbital, levetiracetam, and
have not yet been recognized in veterinary medicine. 5,21 The mor- zonisamide are popular clinical ACD monotherapy choices. 24,28,30
phology of CPTs usually allows for rapid and accurate cytologic Multidrug ACD protocols are frequently needed to control refrac-
diagnosis of tumor type when performed on surgical or MIBB tory seizures in brain tumor patients, and the aggressiveness and
21
specimens. In dogs and humans, CPCs frequently demonstrate diligence of the approach to seizure management is often as
local invasion and commonly metastasize via the ventricular important to the therapeutic outcome as the tumor response to
system. 21 other treatment modalities. 30
Although the genetic and epigenetic studies performed to date Animals that have peritumoral vasogenic edema on MRI are more
in canine brain tumors have identified similarities in molecular likely to respond favorably to corticosteroid treatment (Figs. 31.4A,
signatures, differentially expressed genes, and methylation profiles B and see Fig. 31.1A) however, animals without significant vasogenic
in developmentally regulated genes between human and canine edema may benefit also from the antiinflammatory and euphoric
tumors, these studies were performed with fairly limited microar- effects of corticosteroids; corticosteroid therapy alone may also tran-
ray platforms. 8,10,67–74 It is likely that additional common denom- siently reduce the tumor burden in some cases (see Figs. 31.4A, B)
inators are shared among canine and human tumors and will be or provide modest benefit to animals with tumors causing second-
discovered with the use of more robust whole exome sequencing ary obstructive hydrocephalus. Polyuria, polydipsia, polyphagia, and
7
23
and single nucleotide polymorphism analytical systems. It is also sedation are commonly anticipated and reported adverse effects of
probable that aberrations in key pathways unique to the dog will palliative treatment, but palliative therapies are rarely associated with
10
continue to be revealed. significant treatment-associated morbidity that necessitates discon-
tinuation of therapy. 9,30,78
Cerebrospinal Fluid Analysis Pain associated with nervous system tumors can arise from
CSF analysis provides data that are complementary to clinical compression or stretching of the meninges, nerve roots, or vas-
examination and diagnostic imaging results, and helps the clini- culature, tumor-associated meningitis, neuritis, or radiculitis, and
cian refine the list of differential diagnosis. Obtaining CSF when tumor infiltration of the periosteum or musculature. Hyperes-
44
ICH is present carries a risk of causing clinical deterioration. thesia of the head or neck is frequently observed in dogs with
Although this risk is low, it should be critically assessed in each brain tumors, being reported in 12% of dogs with PBTs in one
patient and evaluated in context of the likelihood of obtaining study. Clinical signs consistent with pain often respond to cor-
2
a nonspecific test result. Advanced imaging of the brain should ticosteroid treatment, and additional opioid or neuropathic pain
always precede CSF collection to best evaluate patient risk. agents can be added if necessary.
Although CSF is a sensitive indicator of intracranial disease Studies published to date indicate that 6% and up to 19%
and is frequently abnormal in patients with brain tumors, white of canine and feline meningiomas, respectively, are identified
2,3
blood cell (WBC) counts, WBC differentials, and total protein incidentally. Given the increasing clinical usage of serial cross-
concentrations are highly variable and are often nonspecific for sectional imaging techniques to manage numerous diseases in vet-
neoplasia. 75,76 In one study of CPTs, CSF analysis was helpful for erinary medicine, it is likely that the frequency of identification of
the differentiation of CPCs from CPPs, as observation of a CSF incidental brain tumors will increase. Thus objective observation
total protein concentration greater than 80 mg/dL was exclusively (e.g., watchful monitoring) also represents a reasonable approach
21
associated with a diagnosis of CPC. Exfoliated neoplastic cells to the management of some small and asymptomatic brain tumors
may be observed in the CSF cytology of patients with any type of (see Figs. 31.4C–E). Further elucidation of the natural disease his-
brain tumor, but choroid plexus tumors, lymphoma, HS, and cats tory for specific brain tumors will be paramount to identifying
with caudal brainstem oligodendrogliomas have been the most optimal indications for watchful monitoring, as well as recom-
frequently reported. 2,21,65,77 mended observation intervals and protocols.
Currently, there is no robust information regarding survival
Treatment and Prognosis of Intracranial Tumors associated with palliative care of specific PBT types or grades.
Pooled data indicates a median survival time (MST) after pallia-
Many veterinary studies regarding the treatment of brain tive care of PBT of approximately 9 weeks, with a range of 1 to
tumors are limited by the inclusion of presumptively diag- 13 weeks. 3,7,9,30,79 Dogs with supratentorial tumors treated pal-
nosed cases, variable survival definitions and end-points, lack liatively have a better prognosis (MST 25 weeks) than those with
30
of inclusion or reporting of objective imaging-based criteria infratentorial tumors (MST 4 weeks). The prognosis associated
of therapeutic response or other unbiased quantitative follow- with palliative care of pituitary tumors is more favorable than
80
up metrics, retrospective study designs, and small case num- PBTs, with a MST of 51 weeks reported in one study.
bers 7,9,78 Thus there currently exists a significant void in the
literature with respect to meaningful data regarding tumor Chemotherapy
type-specific therapeutic outcomes for many PBTs, as well as Data evaluating the efficacy of chemotherapy for the management
a lack of large and rigorously designed trials comparing treat- of brain tumors is limited by the lack of histologic tumor diagno-
ment modalities. ses in the vast majority of reported cases, and the preponderance