BIOLOGIC BEHAVIOUR

General Considerations

•gastric tumors are uncommon and account for < 1% of all cancers

•etiology unknown although chronic nitrosamines administration may cause gastric carcinoma in dogs

Gastric Carcinoma

•gastric ADC is rare in cats but accounts for 42%-72% of all canine gastric tumors

•mean age 8 years, but 19% dogs are < 5 years

•sex predisposition: male with a male-to-female ratio of 2.5:1

•breed predisposition: Belgian Shepherd and Rough-Coated Collie

•location: pyloric antrum or lesser curvature

•3 anatomic descriptions:

•scirrhous due to firm and non-distensible texture = linitis plastica

•plaque-like mucosal lesion with large central ulcer

•raised polypoid lesions

•metastatic rate 74% in dogs with sites including gastric lymph node, peritoneum, liver, lungs, omentum, adrenal glands, duodenum, pancreas, spleen, esophagus, kidneys, diaphragm, myocardium, long bones, pituitary gland, bile duct, brain, and testes

Lymphosarcoma

•LSA is the most common gastric tumor in cats (solitary or multicentric) and most are FeLV negative

•sex predisposition: males

•gross appearance: discrete mass or diffuse gastric wall diffusion

Leiomyoma

•leiomyoma is common in very old dogs and is the 2nd most common gastric tumor in dogs

•mean age 15 years with 82% prevalence in 17-18-year-old Beagles

•discrete solitary lesions (usually pedunculated) in the cardia or gastroesophageal junction causing mass effect

•ulceration is uncommon

Carcinoids

•gastric carcinoids are tumors of the enterochromaffin system and are referred to as amine precursor uptake and decarboxylation tumors or APUDomas

•gastric carcinoids are functional and, in humans, are diagnosed by clinical presentation, measurement of urinary serotonin metabolites, provocative pentagastric testing, radionucleide scans, and CT

•carcinoids are locally invasive, and metastasize to regional lymph nodes, lungs, pleura, and peritoneum

•carcinoids usually occur in geriatric animals and gastric carcinoid has been reported in a 15-year-old cat

Other

•other malignant gastric tumors include FSA, leiomyosarcoma, plasmacytoma, and carcinoid

•metastasis to the liver and duodenum reported in both cases of leiomyosarcoma

•benign gastric tumors include adenoma, leiomyoma, or hypertrophic gastropathy

•adenomatous polyps are usually an incidental finding but they may cause pyloric obstruction

CLINICAL FEATURES

Clinical Signs

•clinical signs are caused by gastric outflow obstruction, altered motility, or chronic blood loss secondary to tumor necrosis and ulceration

•progressive vomiting is common and may contain fresh or digested blood

•weight loss may be caused by poor digestion, protein malnutrition, or cancer cachexia

DIAGNOSIS

Laboratory Tests

•laboratory tests and survey radiographs are usually unrewarding

•leiomyoma and leiomyosarcoma have been associated with paraneoplastic hypoglycemia

•microcytic hypochromic anemia is common with chronic blood loss and occult blood may be detected in feces

•increased liver enzymes may be seen with hepatic metastasis or obstruction of the common bile duct

Imaging

Radiographs

•positive- or double-contrast radiographs: gastric tumors can appear as a mass effect, ulcer crater, delayed gastric emptying with poor motility, and delayed adherence of contrast material to an ulcerated tumor

Ultrasonography

•ultrasonographic findings include transmural thickening of the gastric wall with loss or altered layering (poor echogenic outer and inner lining with hyperechoic central zone)

•other findings include tumor location, ulceration, extension through gastric wall, and lymphadenopathy

•gastric ADC tend to appear as sessile mass located in the lesser curvature or antrum

•benign lesions tend to be either pedunculated or well circumscribed with gastric leiomyoma commonly located in the cardia

Endoscopy

•gastroscopy allows direct visualization and guided biopsy

•several biopsies should be performed as superficial ulceration, necrosis, and inflammation is common

•submucosal masses are difficult to biopsy and false-negative results are common

Other Imaging Techniques

•CT and MRI

TREATMENT

Surgery

General Considerations

•surgery is recommended for gastric ADC and possibly solitary feline gastric LSA but complicated by advanced stage at presentation, frequent metastasis, difficult access, and debilitated animal

•lymph node metastasis is variable and all abdominal lymph node should be evaluated for staging purposes

•curative resection should be attempted if disease is localized to the stomach

•surgical techniques: Billroth I or II or palliative bypass procedures

•Billroth I or II provides immediate relief of gastric outflow obstruction and clinical improvement in early postoperative period

•Billroth II (partial gastrectomy and gastrojejunostomy) or complete gastrectomy (with biliary by-pass) are very extensive surgeries with high morbidity and minimal survival advantage

•partial gastrectomy preferred in humans due to better nutritional status and quality of life and radical gastrectomy does not improve survival time

•palliative gastrojejunostomy for inoperable or metastatic lesions but associated with significant morbidity including anastomotic ulcers

Leiomyoma

•gastrotomy via exploratory ventral midline or lateral intercostal thoracotomy approach

•gastrotomy and submucosal resection recommended with minimal risk of contamination, hemorrhage, or stricture, and good tumor control

Chemotherapy

•no known effective chemotherapy agents for gastric ADC

•gastric LSA does not respond well to conventional chemotherapy protocols and chemotherapy may not be required following surgical resection of solitary gastric LSA in cats

Prognosis

•prognosis depends on surgical excision, tumor type and grade, and presence of metastatic lesions

•prognosis is poor for gastric ADC as majority are dead within 6 months due to either recurrent or metastatic disease

•gastric leiomyosarcoma: MST 12.0-21.3 months, with 1-year survival rate 75% and 2-year survival rate 66%

•54% metastatic rate, but metastasis is not a poor prognostic factor with a MST 21.7 months

•gastric LSA: MST 40 weeks with Madison-Wisconsin protocol and 15.5 months with prednisolone-chlorambucil

•benign lesions and extramedullary plasmacytoma have an excellent prognosis following surgical resection