Page 809 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 34 Miscellaneous Tumors 787

mortality (7%), and short hospitalization stay (1 day). The meso- and/or RT, as nonrandomized observational studies have shown
thelioma case lived the longest of the neoplastic cases, at 107 days. improved survival with multimodal treatment but randomized
321,322
With the tremendous growth in under-
In another study, 58 dogs with idiopathic or malignant pericardial
studies have not.
VetBooks.ir effusion (at least 10 of which were mesotheliomas) treated with standing of the genetic alterations found in mesotheliomas, a
wide array of other novel therapies are under investigation in
thoracoscopic pericardial window or thoracotomy and subtotal
pericardectomy were evaluated. The median disease-free interval randomized clinical trials in humans. 274 Overall, mesothelioma
and MST for dogs with malignant effusions, although short at still carries a poor prognosis. Improved ability to assess an indi-
approximately 3 to 4 months, did not significantly differ between vidual’s tumor’s markers and mutations will help guide therapy,
the two surgical techniques. 311 Thus the less invasive procedure including novel agents, and will hopefully improve survival time
can be considered for palliation of malignant pericardial effu- in the future.
sions. For palliative management of pleural effusion, a permanent
port can be placed that allows for both ease of effusion removal
and administration of intracavitary chemotherapy. 312 The MST SECTION E: NEOPLASIA OF THE HEART
for animals with untreated mesotheliomas in any location is dif-
ficult to assess from reports, as the tumors are rare and animals
frequently are euthanized at the time of diagnosis. JENNA H. BURTON AND JOSHUA A. STERN
Intracavitary cisplatin has shown palliative potential in the
dog; it was well tolerated and greatly decreased mesothelioma- Incidence and Risk Factors
associated thoracic fluid accumulation in three dogs in one Cardiac and pericardial neoplasms are rare in both dogs and cats.
study. 313 The treatments also appeared to arrest tumor growth for The frequency at which dogs were diagnosed with cardiac tumors
a limited time. Two doses of intracavitary carboplatin was safely in a Veterinary Medical Data Base (VMDB) search over a 14-year
administered to a cat with suspected pleural mesothelioma and time frame was 0.19%, with 84% of tumors identified as primary
resulted in transient resolution of clinical signs for a total of 54 cardiac neoplasia. 323 In two canine necropsy series, the frequency
days, at which point the owners discontinued therapy. 314 Unfor- at which primary or metastatic neoplasia was detected ranged
tunately, local penetration of intracavitary chemotherapy occurs from 2.7% to 3.1% of all cases examined and represented 11.7%
only to a limited depth (2–3 mm), and thus large masses will to 28.3% of all cancers diagnosed in these dogs at necropsy. 324,325
not be affected significantly, other than from ultimate exposure Reports are conflicting as to whether primary or metastatic tumors
to the systemically absorbed intracavitary drug. In such cases, predominate in dogs as the reported frequency of secondary car-
combining debulking surgery or systemic chemotherapy such as diac tumors ranges from 16% to 86%. 323–326 Cardiac metastases
DOX or mitoxantrone with intracavitary cisplatin may be ben- may be common in dogs with advanced stage cancer, but remain
eficial. For peritoneal mesothelioma, four doses of intracavitary clinically silent and challenging to diagnosis antemortem, leading
cisplatin in two dogs and carboplatin in one cat, combined with to likely underreporting of these events except when necropsy is
piroxicam administration, resolved the effusion in all cases. 315 performed. 326–328
One of the dogs had debulking surgery first; this dog was still in Cardiac tumors generally occur in middle-aged to older
remission at 2 years, whereas the other dog and the cat lived 8 dogs. 323–326 Hemangiosarcoma (HSA) is the most common pri-
and 6 months, respectively. IV chemotherapy may provide bene- mary heart tumor in dogs, followed by aortic body tumors (ABTs)
fit in some patients; single-agent IV cisplatin administered every such as chemodectomas and paragangliomas. HSA and ABT rep-
3 weeks was reported to improve clinical signs in a dog with resent 40% to 69% and 8% to 28% of all primary cardiac tumors
bicavitary epithelial mesothelioma, until sudden death occurred in VMDB and necropsy studies, respectively. 323,325,326,329 Breeds
5 months after treatment initiation. 316 potentially at increased risk for cardiac HSA include golden
retrievers and German shepherds; boxers, Labrador retrievers,
Comparative Aspects and cocker spaniels are commonly reported to develop cardiac
HSA as well. 323,324,330–332 ABTs occur most frequently in older
In humans, approximately 70% to 80% of mesotheliomas are brachycephalic breeds, such as bulldogs, boxers, and Boston terri-
linked to occupational exposure to aerosolized asbestos fibers, ers, and it has been suggested that chronic hypoxia may stimulate
with the type of employment, such as construction work, ship development of these tumors in brachycephalic breeds; 323,333–335
building, heating trades, and insulation work significantly increas- however, nonbrachycephalic breeds such as German shepherds,
ing relative risk. 317 There is a long latency period from time of Labrador retrievers, and golden retrievers also develop ABT at
exposure to tumor development, ranging from 12 to 50 years. Less increased frequency and not all brachycephalic breeds develop
often, several naturally occurring minerals with elongated struc- ABT, which suggests other factors likely contribute to its
tures, termed naturally occurring asbestos (NOA), are associated pathogenesis. 323,336,337
with mesothelioma development. These cases are seen in regional Cardiac tumors are even less common in cats, with an over-
populations in many sites worldwide, affect men and women all incidence of 0.0275% in a VMDB search. 338 Cardiac lym-
equally, and have a younger age at onset compared with occupa- phoma, both primary and secondary, predominates. 326,339,340
tional exposure cases. 318 As with other forms of lymphoma, feline leukemia virus (FeLV)
In humans with mesothelioma, the median survival is infection likely plays a role in cardiac lymphomagenesis in
approximately 1 year from symptom onset. Prognosis is asso- cats. 326,339 Several case reports of ABT in cats exist and cardiac
ciated with the histologic subtype, and multiple other factors HSA is rare. 326,341–346
have been assessed to refine prognosis, stratify patients for clini-
cal trials, and guide targeted therapies. 274,319,320 Chemotherapy, Pathology and Natural Behavior
specifically pemetrexed or raltitrexed, combined with cisplatin
or carboplatin, is the standard of care firstline therapy. 321 There Tumors of the heart may occur at the heart base or in pericar-
is ongoing controversy regarding the therapeutic role of surgery dial, intracavitary, or intramural locations. Primary tumors may