Gastric neoplasms in dogs and cats (Proceedings)

Overview

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 pathophysiology

The 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.

Clinical features

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.

Definitive diagnosis of stomach tumors is based on cytological or histological demonstration of neoplastic cells. Ultrasound-guided needle aspiration cytology of a thick gastric wall can provide a diagnosis of lymphosarcoma in dogs and cats, and occasionally be strongly suggestive of adenocarcinoma. Enlarged abdominal lymph nodes, or nodules in the liver and spleen are also candidates for aspiration and can provide cells for definitive diagnosis, and further stage the patient. Biopsies for histopathology can be obtained by endoscopy, or during surgical exploration of the abdomen. Some infiltrative forms of gastric neoplasia may lie beneath a normal gastric mucosa or beneath an ulcer bed making diagnosis by endoscopic biopsy difficult in some patients. Confirmation of a diagnosis in such animals may require surgically acquired biopsies.

Patients that are suspected of gastric tumors should be clinically staged with abdominal imaging, ideally abdominal ultrasound, and thoracic radiographs. Nodules observed ultrasonographically in other organs, or enlarged abdominal lymph nodes, may be aspirated as noted above for cytological examination to assess for metastasis. It is important to remember that negative results of any staging procedure do not guarantee an absence of tumor. The role of advanced cross sectional abdominal imaging (abdominal computed tomography or magnetic resonance imaging) for staging patients suspected of having gastric tumors needs to be explored. Thoracic CT scans are more sensitive for detection of pulmonary metastasis and could be considered where available prior to taking an animal with suspected gastric neoplasia to surgery.

Treatment

Surgical resection is the preferred treatment of dogs with gastric adenocarcinomas, smooth muscle tumors, or extramedullary plasmacytomas, particularly for those without overt evidence of metastatic disease. Locally extensive disease and/or metastatic disease in most patients with adenocarcinoma precludes surgical cure, but surgery may still be of palliative benefit for the relief of gastric obstruction if present. Reliably effective chemotherapeutic protocols for gastric adenocarcinomas have not been established, although many agents have been tried. Surgical resection is also the treatment of choice for dogs with tumors originating from smooth muscle.

Chemotherapy is the preferred treatment approach to both dogs and cats with gastric lymphoma. Multiple protocols have been given to dogs and cats with gastric lymphosarcoma. The type of protocol selected is often influenced, especially in cats, by the grade of the lymphosarcoma. Consultation with a veterinary oncologist can be of great value in deciding the best chemotherapeutic approach to the patient with gastric lymphosarcoma. Intestinal tract extramedullary plasmacytomas have been treated with prednisone and melphalan, particularly when there is evidence of incomplete resection or loco-regional metastatic disease.

In cases in which surgery is not possible or declined, consideration can be given to therapy using a non-steroidal anti-inflammatory drug (NSAID), particularly for those patients that could have carcinomas. Such a treatment approach needs to be carefully considered because of the increased risk of mucosal ulceration created by some NSAIDs as these animals are already at risk of mucosal ulceration, and it should be emphasized that the role of NSAIDs in the treatment of dogs with gastric neoplasms, particularly gastric adenocarcinomas, has not been investigated. Whether concurrent administration of a prostaglandin analogue such as misoprostol would reduce the risk of ulcer created by NSAID therapy in patients with gastric neoplasms has not been studied. Larger, prospective clinical studies of the role for NSAIDs in treating dogs with intestinal epithelial neoplasms, both benign and malignant, are needed.

Prognosis

Gastric adenocarcinoma carries a poor to grave prognosis. Most patients have extensive local disease or metastasis at the time of diagnosis. Gastric lymphosarcoma is associated with a variable prognosis. Cats with low-grade forms of the disease tend to have longer survival times than cats with higher grade lymphosarcoma. Some consider that focal gastric lymphosarcoma may carry a better prognosis than more diffuse gastrointestinal involvement. Patients with gastric leiomyomas or leiomyosarcomas, or extramedullary plasmacytomas can have a good prognosis with complete resection of the tumor and if there is no evidence of metastatic disease. The prognostic value of histological grade of gastric leiomyosarcomas has not been determined as has been for soft tissue sarcomas in other anatomical locations.

References

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