Gastric neoplasms in dogs and cats (Proceedings)
Primary gastric neoplasia is an important differential diagnosis for a dog or cat with vomiting, especially chronic vomiting, anorexia and weight loss, particularly animals that are middle-aged and older. Because animals, especially dogs with gastric adenocarcinomas, have extensive disease at the time of definitive diagnosis, the prognosis is typically poor, emphasizing the need for not only early diagnosis, but improved treatment options for affected patients.
Etiology and pathophysiologyThe most common primary gastric tumor in dogs is adenocarcinoma in various forms; lymphosarcoma and smooth muscle tumors (leiomyomas, leiomyosarcomas) are considered the next most common tumors. Dogs with gastric tumors are most commonly middle-aged to older dogs. The antrum and lesser curvature are the most common sites in which adenocarcinomas are found in dogs. Common metastatic sites of gastric adenocarcinomas include regional lymph nodes, liver, spleen, omentum/peritoneal cavity, and lung.
The most common primary gastric tumor in cats is lymphosarcoma, which can have a diverse array of appearances from infiltrative to polypoid lesions. Gastric adenocarcinomas can be seen in cats, but are considered rare.
In both dogs and cats, gastric lymphosarcoma is commonly a part of more diffuse gastrointestinal lymphosarcoma, but can be seen as a solitary tumor in the stomach. Extramedullary plasmacytomas have been described in both dogs and cats as primary gastric tumors.
Ulceration of the gastric mucosa is a common feature of stomach tumors, but will not be present in all patients. In patients with gastric bleeding secondary to gastric ulceration, chronic blood loss can lead to iron deficiency anemia. Iron deficiency anemia can be either regenerative or non-regenerative.
Patients with primary gastric neoplasms most commonly present with a history of vomiting; hematemesis and melena may be seen in some. Anorexia and weight loss are also common clinical signs.
The physical examination in most patients is not overtly suggestive of gastric neoplasia; some cats may have palpable masses in the cranial abdomen. Poor body condition reflecting weight loss is a somewhat common physical examination finding in the author's experience. Animals that have developed anemia secondary to neoplasm-associated gastric ulceration may have pale mucous membranes.
For most patients, obtaining results of routine laboratory testing (CBC, biochemical profile, urinalysis, fecal flotation) helps exclude non-gastrointestinal origins of vomiting such as hepatic, renal or adrenal gland disease. Results of laboratory testing are not always helpful and can, in some cases, be confusing (e.g. pre-renal azotemia and an increase in BUN disproportionate to the serum creatinine, which can reflect gastrointestinal bleeding).
Anemia, which can be regenerative or non-regenerative, and may have features of iron deficiency (microcytosis, hypochromasia), may be seen in patients with erosive gastric tumors; anemia could also reflect chronic inflammatory disease. Obtaining erythrocyte indices and reticulocyte counts, and examination of blood smears are important in the evaluation of patients with anemia. Inflammatory leukograms (mature neutrophilia, monocytosis) and thrombocytosis are also possible on the CBC. Biochemical profile results are usually normal unless there has been large scale gastric bleeding, in which case decreases in albumin and total protein are possible, as well as increases in BUN without increases in creatinine. Increases in liver enzyme activities may be seen in animals with hepatic metastasis.
Hypoglycemia has been described as a paraneoplastic phenomenon in dogs with gastric leiomyomas or leiomyosarcomas; polyuria and polydipsia have also been seen as paraneoplastic syndromes associated with these smooth muscle tumors.
Suspicion of a gastric tumor can be raised by plain or contrast radiographs, or abdominal ultrasonography. Radiographic findings may include thickened gastric wall, displacement of the stomach, filling defects and mucosal irregularity (contrast studies), and hypomotility or gastric obstruction (contrast studies). Ultrasonographic features of gastric tumors include gastric wall thickening, which can be focal or somewhat diffuse, focal gastric masses, mucosal craters that suggest ulceration, disruption of the normal layering of the gastric wall, and poor motility. There may be enlargement of regional lymph nodes as a consequence of either hyperplasia secondary to inflammation or metastasis to these regional lymph nodes. Nodules in the liver or spleen may be indicative of metastatic disease.
Endoscopic findings in animals with gastric tumors include ulcers and erosions, polypoid lesions, obvious thickening of the gastric wall (usually best appreciated in the incisura angularis), inability to distend the stomach with air, and retention or prominence of rugal folds. A normal appearance to the gastric mucosa during endoscopic examination does not rule out a gastric neoplasm as some tumors may be deep to the gastric mucosa.