Page 474 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

452 PART IV Specific Malignancies in the Small Animal Patient

imminent or present gastrointestinal or common bile duct
obstruction, respectively. Radiation therapy and chemother- SECTION E: GASTRIC CANCER
apy have shown limited value in humans and animals. Occa-
VetBooks.ir sionally, uncomfortable effusions from carcinomatosis can be OWEN T. SKINNER
diminished with systemic or intracavitary chemotherapy (see
Chapter 12); however, the palliative response tends to be short
lived. Incidence and Risk Factors

Prognosis Gastric cancer is rare in small animals, comprising 0.16% of cancers
in one large study. 281 The causes of gastric cancers have not been
The outlook for this disease in companion species is very poor identified in dogs. 281–284 Gastric carcinoma has been experimentally
because of its critical location and advanced stage at diagnosis. In induced in dogs with nitrosamines; however, the clinical relevance
a recent study evaluating the outcome for 34 cats with pancreatic of these findings is unclear. 285 Hypergastrinemia is a risk factor in
carcinoma, the overall median survival time was 97 days and, for humans, typically associated with atrophic gastritis caused by Heli-
cats treated with either chemotherapy or surgery, the median sur- cobacter pylori. 286 Although gastrin levels have not been reported to
vival time was 165 days. 265 Cats with abdominal effusion at diag- be increased in small populations of dogs with gastric carcinoma,
nosis survived a median of 30 days. 265 Only three cats survived individual dogs have been noted with substantial increases in serum
greater than 1 year. 265 gastrin. 287,288 H. pylori infection is rare in dogs. 289 Non–H. pylori
Helicobacter species are highly prevalent in dogs, although the clini-
Comparative Aspects 277–279 cal significance of these organisms is uncertain, with both mild gas-
tritis and asymptomatic presentations reported. 289–291
Pancreatic exocrine carcinoma accounted for an estimated 53,670 Gastric carcinoma is the most common nonhematopoietic gas-
new cases and 43,090 deaths in the United States in 2017. 278 Sev- tric tumor in dogs. 292–294 Breeds at higher risk of gastric carci-
eral risk factors have been identified, including older age, inherited noma include the Tervueren, Bouvier des Flandres, Groenendael,
susceptibility, cigarette smoking, obesity, and diabetes mellitus. collie, standard poodle, Norwegian elkhound, and Norwegian
Most patients have disease progression beyond the pancreas at the lundehund. 281,287,295–297 Mean age at presentation is typically 8
time of initial diagnosis. Seventy-five percent are located in the to 10 years. 281,283,284,293,294 Male dogs are consistently overrepre-
head of the pancreas and the remainder in the body and tail of the sented, with a male-to-female ratio of approximately 1.5:1. 281,292–
pancreas. Direct extension to duodenum, bile duct, and stomach, 294,298 The most common mesenchymal tumors of the stomach
as well as common metastasis to LNs and liver, make treatment are smooth muscle tumors (leiomyomas and leiomyosarcomas)
difficult. and gastrointestinal stromal tumors (GISTs). These occur with
Treatments that are currently used include surgery (curative similar frequency in male and female dogs, with a mean age at
or palliative), radiotherapy (as an adjuvant or for treatment of diagnosis of approximately 11 years. 299 Other reported canine
advanced local disease), and systemic chemotherapy. Surgical gastric tumors include mast cell tumor (MCT), 300 histiocytic sar-
resection is the mainstay of treatment for pancreatic carcinoma coma, 301,302 plasmacytoma, 303 and undifferentiated sarcoma. 304
in humans, especially if the patient has a small tumor localized Lymphoma is the most common primary gastric malignancy in
to the pancreas. Depending on the extent of disease within the cats. 305 Gastric carcinoma is rare in cats, representing fewer than
pancreas, other surgical procedures include pancreaticoduode- 5% of feline gastrointestinal carcinoma cases. 306–308 Gastritis and
nectomy (Whipple’s procedure) or total pancreatectomy. With Helicobacter have been proposed as risk factors for feline gastric car-
recent advances in surgical technique, the mortality associated cinoma and lymphoma. 309,310 Other reported feline gastric tumors
with these procedures has decreased; however, considerable include MCT, 311 carcinoid, 312 hamartoma, 313 and polyps. 314
patient morbidity still exists. Removal of the entire pancreas
necessitates management of the patient for exocrine pancreatic Pathology and Natural Behavior
insufficiency and diabetes mellitus. After surgery, chemotherapy
is recommended to improve survival, but there is no superior Gastric carcinoma is classified as either “intestinal” (with papillary,
single chemotherapeutic approach. In patients whose tumors are acinar, or solid subtypes) or “diffuse” (with undifferentiated or glan-
determined to be borderline resectable, chemotherapy is admin- dular subtypes). 298,315 Intestinal type tumors in humans are thought
istered for 2 to 4 months and then, if the patient is still free to arise from sequential progression through gastritis, metaplasia,
from metastases, surgery or chemoradiation can be considered. and dysplasia, whereas diffuse type tumors may be associated with
Treatments for locally advanced or widely metastatic disease are mutation or methylation of CDH1. 316 The diffuse histologic type
palliative, but include chemotherapy alone or chemoradiation. is more common in dogs. 283,287,298 Canine gastric carcinoma com-
If biliary outflow is obstructed, several procedures may be indi- monly arises in the pylorus or lesser curvature, although some car-
cated including surgical bypass, endoscopic biliary stenting, or cinomas may lead to diffuse, firm thickening of the stomach (linitis
percutaneous biliary decompression. Palliative bypass of gastric plastica). 281,293,296,298,317 Ulceration is common and may progress to
outflow obstruction can be performed by open gastrojejunos- full-thickness perforation and peritonitis. 294 Metastasis to regional
tomy, laparoscopic gastrojejunostomy, duodenal stenting, or LNs is common (32% at presentation and 77% at postmortem),
decompressive gastrostomy tube. Despite recent developments with liver and lungs less frequently affected. 292,298
and research into treatment of this disease, the prognosis remains Many mesenchymal tumors previously diagnosed as leio-
poor, with overall 5-year survival rates for all patients less than myosarcomas have been reclassified as GISTs. 299,304 Gastric
6%. 280 leiomyoma and leiomyosarcoma are typically focal, with or