Gastric Neoplasia

Gastric neoplasia refers to the abnormal, uncontrolled growth of cells within the stomach wall, encompassing a diverse group of benign and malignant tumors. In veterinary surgical oncology, gastric tumors are relatively uncommon but clinically significant due to their often advanced stage at diagnosis and guarded prognosis. The stomach, as a hollow organ, can give rise to neoplasms from any of its constituent layers: the mucosa (epithelial tumors such as adenomas and adenocarcinomas), the submucosa (lymphoid tissue leading to lymphoma), the muscularis propria (leiomyomas and leiomyosarcomas), and the interstitial cells of Cajal (gastrointestinal stromal tumors, GISTs). Surgical management is central to the treatment of localized gastric tumors, with techniques ranging from partial-thickness resection (mucosal resection) to full-thickness wedge resection, partial gastrectomy (Billroth I or II), or total gastrectomy in rare cases. The surgical approach must be tailored to tumor location, size, depth of invasion, and histologic type, with the goal of achieving complete margins (R0 resection) while preserving gastric function. Gastric neoplasia can cause significant morbidity through mechanical obstruction, bleeding, ulceration, and perforation, and may be associated with paraneoplastic syndromes. A thorough understanding of gastric anatomy, vascular supply, and lymphatic drainage is essential for safe surgical resection and reconstruction.

The exact etiology of gastric neoplasia in dogs and cats is largely unknown, but several factors have been implicated. Chronic inflammation is a recognized precursor for gastric adenocarcinoma in humans (Helicobacter pylori-associated gastritis) and is suspected in animals, although a direct causal link has not been definitively established. In dogs, chronic gastritis, gastric ulceration, and prolonged administration of non-steroidal anti-inflammatory drugs (NSAIDs) may predispose to mucosal injury and subsequent neoplastic transformation. Genetic mutations, including alterations in tumor suppressor genes (e.g., p53) and oncogenes (e.g., KIT in GISTs), play a role in the pathogenesis of specific tumor types. For example, mutations in the c-KIT proto-oncogene are implicated in the development of gastrointestinal stromal tumors (GISTs) in dogs, similar to humans. Environmental factors, such as dietary carcinogens (nitrosamines, heterocyclic amines) and exposure to certain toxins, have been hypothesized but not proven. Viral etiologies, such as Epstein-Barr virus in human gastric cancer, have not been confirmed in veterinary species. In cats, gastric lymphoma is often associated with feline leukemia virus (FeLV) infection, although the incidence has decreased with vaccination. Additionally, immune-mediated and hormonal factors may contribute to the development of gastric polyps and other benign neoplasms. Overall, the etiology is likely multifactorial, involving an interplay of genetic predisposition, chronic inflammation, and environmental triggers.

Gastric neoplasia is relatively uncommon in dogs and cats compared to other gastrointestinal tumors, accounting for less than 1% of all canine neoplasms and approximately 0.5-1% of feline neoplasms. In dogs, gastric adenocarcinoma is the most common malignant gastric tumor, representing 40-50% of all gastric neoplasms, followed by leiomyosarcoma (20-30%) and lymphoma (10-20%). Benign tumors, such as leiomyomas and adenomatous polyps, are less frequently diagnosed. Gastric lymphoma is more common in cats than in dogs, and in cats, it is often part of multicentric lymphoma, with the stomach being a common site of alimentary lymphoma. Breed predispositions have been reported: gastric adenocarcinoma is more common in certain breeds, including Belgian Shepherd Dogs, Chow Chows, and Rough Collies, suggesting a genetic component. Leiomyosarcomas are more frequently seen in large-breed dogs, particularly German Shepherd Dogs and Golden Retrievers. Gastric lymphoma in cats is more common in domestic shorthair cats, and older cats (mean age 9-10 years) are at higher risk. Age is a significant factor: most gastric tumors occur in middle-aged to older animals, with a mean age of 8-10 years in dogs and 10-12 years in cats. Sex predilection is variable; some studies report a slight male predominance for gastric adenocarcinoma, while others show no sex difference. No significant activity or working dog predispositions have been identified, but chronic gastritis and NSAID use may increase risk.

The pathophysiology of gastric neoplasia involves a complex cascade of cellular and molecular events leading to uncontrolled proliferation, invasion, and metastasis. Initially, genetic mutations (e.g., in oncogenes, tumor suppressor genes, or DNA repair genes) cause dysregulation of cell cycle checkpoints, apoptosis, and differentiation. In gastric adenocarcinoma, the progression from chronic gastritis to atrophy, intestinal metaplasia, and dysplasia is a well-described pathway in humans and is likely similar in dogs. The tumor arises from gastric epithelial cells and invades the lamina propria, submucosa, and muscularis propria, eventually penetrating the serosa. As the tumor grows, it can cause mechanical obstruction of the pylorus or cardia, leading to gastric outflow obstruction and delayed gastric emptying. Ulceration of the tumor surface can result in chronic blood loss, leading to iron-deficiency anemia, or acute hemorrhage causing hematemesis and melena. Tumor necrosis and inflammation can lead to gastric perforation, causing septic peritonitis. Malignant tumors, particularly adenocarcinomas and leiomyosarcomas, have a high metastatic potential, spreading via the lymphatic system to regional lymph nodes (gastric, hepatic, splenic) and via the bloodstream to the liver, lungs, and other organs. Lymphoma, being a systemic disease, can involve the stomach as part of multicentric or alimentary forms, with infiltration of the gastric wall by neoplastic lymphocytes, leading to thickening, loss of motility, and malabsorption. Paraneoplastic syndromes, such as cachexia, anemia, and coagulopathies, may occur due to tumor-derived cytokines and growth factors. The tumor microenvironment, including inflammatory cells, fibroblasts, and angiogenesis, plays a crucial role in tumor progression and metastasis.

Several intrinsic and extrinsic factors predispose animals to gastric neoplasia. Intrinsic factors include breed and genetic predisposition, as seen in Belgian Shepherd Dogs and Chow Chows for adenocarcinoma, and German Shepherd Dogs for leiomyosarcoma. Age is a significant intrinsic factor, with older animals being more susceptible due to accumulated genetic damage and decreased immune surveillance. Sex may play a role, with some studies suggesting a male predominance for gastric adenocarcinoma. Chronic gastritis, particularly lymphocytic-plasmacytic gastritis, is a known risk factor for gastric adenocarcinoma in humans and is suspected in dogs. Gastric ulceration, often due to NSAID administration, can lead to mucosal injury and repair, increasing the risk of neoplastic transformation. Extrinsic factors include dietary habits, such as high intake of processed foods, nitrosamines, and other carcinogens, although evidence in veterinary medicine is limited. Environmental exposure to toxins, such as pesticides and herbicides, may also contribute. Prior gastric surgery, such as gastrotomy or gastropexy, has been hypothesized to increase risk due to chronic inflammation and scarring, but this is not well-documented. In cats, FeLV infection is a significant risk factor for gastric lymphoma, and immunosuppression from any cause may increase susceptibility to lymphoma. Obesity and high-fat diets have been associated with increased risk of gastric cancer in humans, but similar associations have not been confirmed in dogs and cats.

Clinical signs of gastric neoplasia are often nonspecific and may be insidious in onset, leading to delayed diagnosis. Common signs include chronic vomiting, which may be intermittent or progressive, and can contain blood (hematemesis) or be described as coffee-ground material. Weight loss is frequently observed, often despite a normal or increased appetite, due to malabsorption and tumor cachexia. Anorexia or decreased appetite may occur, especially in advanced stages. Lethargy and weakness are common, often due to anemia from chronic blood loss. Melena (dark, tarry stools) may be present if there is significant gastrointestinal bleeding. Abdominal pain may be evident on palpation, and a cranial abdominal mass may be palpable in some cases, particularly with large tumors. In cases of gastric outflow obstruction, animals may exhibit frequent vomiting after eating, leading to dehydration and electrolyte imbalances (e.g., hypochloremia, hypokalemia, metabolic alkalosis). If gastric perforation occurs, acute signs of septic peritonitis, such as severe abdominal pain, fever, and cardiovascular collapse, may develop. Paraneoplastic syndromes, such as hypertrophic osteopathy (in cases of pulmonary metastasis) or hypercalcemia (in lymphoma), may also be present. Physical examination may reveal pale mucous membranes, poor body condition, and signs of dehydration. In cats with lymphoma, palpation may reveal thickened intestinal loops or enlarged abdominal lymph nodes.

The differential diagnoses for gastric neoplasia include a wide range of conditions that cause chronic vomiting, weight loss, and gastrointestinal bleeding. Key differentials include: 1) Chronic gastritis (lymphocytic-plasmacytic, eosinophilic, or Helicobacter-associated), which can mimic the clinical signs but is typically non-neoplastic and may respond to dietary and medical management. 2) Gastric ulceration (due to NSAIDs, stress, or mast cell tumors), which can cause hematemesis and melena; diagnosis is via endoscopy and biopsy. 3) Gastric polyps (benign adenomatous or hyperplastic), which may cause similar signs but are usually benign and can be removed endoscopically or surgically. 4) Pyloric stenosis (congenital or acquired), which causes outflow obstruction and vomiting, but is not neoplastic; imaging and endoscopy can differentiate. 5) Foreign body ingestion, which can cause partial or complete obstruction, with acute onset of vomiting; radiography or ultrasound can identify a foreign body. 6) Inflammatory bowel disease (IBD), which can cause chronic vomiting and weight loss, but is typically managed medically; histopathology is needed for differentiation. 7) Gastrointestinal lymphoma (if the stomach is involved, it is a differential for gastric neoplasia, but it is a type of gastric neoplasia; however, it may be considered separately in terms of treatment). 8) Gastric dilatation-volvulus (GDV), which is an acute, life-threatening condition with severe abdominal distension and non-productive vomiting; radiography shows a gas-filled stomach. 9) Pancreatitis, which can cause vomiting and abdominal pain, but is usually acute and associated with elevated pancreatic enzymes. 10) Liver disease (e.g., hepatic neoplasia or hepatitis), which can cause vomiting and weight loss; liver function tests and imaging are helpful. Definitive diagnosis requires imaging (radiography, ultrasound, CT) and endoscopic biopsy or surgical biopsy.

The diagnostic algorithm for gastric neoplasia begins with a thorough history and physical examination, focusing on the duration and character of vomiting, presence of hematemesis or melena, weight loss, and abdominal palpation. Initial laboratory tests include a complete blood count (CBC), serum biochemistry profile, urinalysis, and possibly a coagulation panel. Anemia (regenerative or non-regenerative) may be present due to chronic blood loss. Biochemistry may reveal hypoalbuminemia, elevated liver enzymes (if metastasis), or electrolyte imbalances (hypochloremia, hypokalemia) due to vomiting. Next, abdominal radiographs (survey and contrast) may show a soft tissue mass, gastric wall thickening, or signs of obstruction, but are often nonspecific. Abdominal ultrasonography is more sensitive and can reveal gastric wall thickening, loss of normal layering, a mass lesion, or regional lymphadenopathy. Ultrasound-guided fine-needle aspiration (FNA) of the gastric wall or mass can be performed for cytology, but may not provide a definitive diagnosis for some tumors. Upper gastrointestinal endoscopy is the gold standard for diagnosis, allowing direct visualization of the gastric mucosa, identification of masses, ulcers, or infiltrative lesions, and procurement of multiple biopsy samples. Endoscopic biopsies are essential for histopathologic diagnosis and grading. If endoscopic biopsy is inconclusive or if the tumor is suspected to be deep (e.g., leiomyosarcoma), surgical biopsy (full-thickness) may be necessary. Computed tomography (CT) is increasingly used for staging, providing detailed information on tumor extent, local invasion, and metastasis to lymph nodes and other organs. CT is particularly useful for surgical planning. In cases where surgery is planned, a thorough staging workup, including thoracic radiographs (to rule out pulmonary metastasis) and abdominal ultrasound or CT, is essential. Exploratory laparotomy may be both diagnostic and therapeutic, allowing for biopsy and resection.

Laboratory findings in gastric neoplasia are often nonspecific but can provide supportive evidence and help assess the patient's overall health. Complete blood count (CBC) may reveal anemia, which can be microcytic and hypochromic (iron deficiency) due to chronic blood loss, or normocytic and normochromic (anemia of chronic disease). Leukocytosis may be present if there is inflammation or infection. Thrombocytopenia may occur in cases of disseminated intravascular coagulation (DIC) or bone marrow metastasis. Serum biochemistry profile may show hypoalbuminemia due to protein-losing enteropathy or malnutrition. Liver enzyme elevations (ALT, ALP) may indicate hepatic metastasis or concurrent hepatobiliary disease. Electrolyte imbalances, particularly hypochloremia, hypokalemia, and metabolic alkalosis, are common in animals with chronic vomiting due to loss of hydrogen and chloride ions. Blood urea nitrogen (BUN) may be elevated if there is dehydration or gastrointestinal bleeding (prerenal azotemia). Urinalysis may reveal a low urine specific gravity if the animal is dehydrated, and the presence of bilirubinuria may indicate hemolysis or liver disease. Coagulation panel (PT, aPTT, platelet count, and possibly D-dimer or antithrombin III) is recommended, especially if surgery is planned, to rule out coagulopathies. Inflammatory biomarkers such as C-reactive protein (CRP) may be elevated in inflammatory or neoplastic conditions. In cats, testing for feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) is recommended, as these are risk factors for lymphoma. Serum gastrin levels may be measured if gastrinoma is suspected, although this is rare. Cytology of fine-needle aspirates from the gastric mass or enlarged lymph nodes may show neoplastic cells, but histopathology is required for definitive diagnosis.

Imaging plays a crucial role in the diagnosis and staging of gastric neoplasia. Survey abdominal radiographs may show a soft tissue mass in the cranial abdomen, gastric wall thickening, or signs of gastric outflow obstruction (e.g., a gas-filled stomach). However, radiographs are often normal in early disease. Contrast radiography (barium swallow) can reveal filling defects, mucosal irregularities, or delayed gastric emptying, but has largely been replaced by endoscopy and ultrasound. Abdominal ultrasonography is highly sensitive for detecting gastric wall thickening, loss of normal wall layering, and intramural masses. It can also identify regional lymphadenopathy, hepatic metastasis, and other abdominal abnormalities. Ultrasound-guided fine-needle aspiration of the gastric wall or mass can be performed for cytology. Computed tomography (CT) provides superior detail and is excellent for surgical planning. CT can accurately assess the extent of gastric wall involvement, the presence of transmural invasion, and the relationship of the tumor to adjacent structures (e.g., liver, pancreas, spleen). CT is also the best modality for detecting lymph node metastasis and distant metastasis to the liver, lungs, and other organs. Three-dimensional reconstructions can be helpful for planning surgical resection. Magnetic resonance imaging (MRI) is rarely used for gastric tumors but may be helpful in assessing soft tissue extension. Thoracic radiographs (three views) are essential to rule out pulmonary metastasis. In cases of suspected lymphoma, abdominal ultrasound and CT are useful for staging, and thoracic radiographs are also recommended. Endoscopic ultrasound (EUS) is not commonly used in veterinary medicine but can provide detailed information on tumor depth and lymph node involvement. Overall, a combination of ultrasound and CT is recommended for comprehensive staging.

Cytology and histopathology are essential for definitive diagnosis and grading of gastric neoplasia. Fine-needle aspiration (FNA) of gastric masses or thickened gastric wall can be performed under ultrasound guidance or during endoscopy. Cytologic evaluation may reveal epithelial cells with criteria of malignancy (e.g., anisocytosis, anisokaryosis, prominent nucleoli) in cases of adenocarcinoma, or a monomorphic population of large lymphoid cells in lymphoma. However, FNA has limited sensitivity for mesenchymal tumors (e.g., leiomyosarcoma, GIST) because the cells may not exfoliate well. Histopathology from endoscopic biopsies or surgical full-thickness biopsies is the gold standard. Endoscopic biopsies are often superficial and may not capture the full depth of the tumor, especially for submucosal tumors. Therefore, if endoscopic biopsies are inconclusive, surgical biopsy is recommended. Histopathologic features of gastric adenocarcinoma include atypical glandular structures, desmoplasia, and invasion into the gastric wall. Leiomyosarcoma is characterized by interlacing bundles of spindle cells with variable mitotic activity and nuclear atypia. GISTs are diagnosed based on immunohistochemical staining for KIT (CD117) and DOG1. Lymphoma shows diffuse infiltration of the gastric wall by neoplastic lymphocytes, which can be classified as B-cell or T-cell based on immunophenotyping. Histopathologic grading (e.g., mitotic index, degree of differentiation) is important for prognosis. Surgical margins should be evaluated for completeness of resection (R0 vs. R1 vs. R2). Special stains, such as Alcian blue for mucin production in adenocarcinomas, and immunohistochemistry for vimentin, smooth muscle actin, and desmin, can help differentiate tumor types. In cases of gastric lymphoma, immunophenotyping (B-cell vs. T-cell) and clonality testing (PARR) may be performed to confirm malignancy and guide treatment.

The treatment of gastric neoplasia is primarily surgical, with the goal of complete resection of the tumor with clean margins. The specific surgical technique depends on the tumor location, size, and depth of invasion. For small, superficial tumors (e.g., adenomatous polyps), endoscopic mucosal resection or surgical gastrotomy with mucosal resection may be sufficient. For larger or full-thickness tumors, a wedge resection (partial gastrectomy) is often performed. This involves excising the tumor with a margin of normal tissue and closing the defect in two layers (e.g., simple continuous pattern with absorbable monofilament suture such as polydioxanone or polyglyconate). For tumors located in the pyloric region, a Billroth I (gastroduodenostomy) or Billroth II (gastrojejunostomy) procedure may be necessary to bypass the pylorus and maintain gastric outflow. For tumors involving the cardia or fundus, a partial gastrectomy with reconstruction may be performed. Total gastrectomy is rarely indicated due to the high morbidity and poor quality of life, but may be considered for diffuse tumors. In cases of gastric lymphoma, surgery is not the primary treatment; instead, systemic chemotherapy (e.g., CHOP protocol) is the mainstay, with surgery reserved for complications such as perforation or obstruction. For benign tumors (e.g., leiomyoma), surgical excision is curative. Preoperative stabilization is crucial: animals with dehydration, electrolyte imbalances, or anemia should be stabilized with intravenous fluids, electrolyte supplementation, and blood transfusion if necessary. Perioperative antibiotics (e.g., cefazolin 22 mg/kg IV at induction and every 90 minutes during surgery) are recommended. Postoperative care includes pain management (e.g., opioids such as methadone 0.2-0.5 mg/kg IV q4-6h, or fentanyl CRI at 2-5 mcg/kg/h), antiemetics (e.g., maropitant 1 mg/kg SC q24h), and nutritional support (early enteral feeding via esophagostomy or gastrostomy tube if needed). The surgical approach is typically a ventral midline celiotomy, with careful exploration of the abdominal cavity to assess for metastasis. The stomach is mobilized, and the tumor is identified. The gastroepiploic and gastric arteries must be preserved to ensure adequate blood supply to the remaining stomach. The surgical technique must be meticulous to prevent leakage and peritonitis.

The prognosis for gastric neoplasia varies widely depending on the tumor type, stage, and completeness of surgical resection. For benign tumors such as leiomyomas, surgical excision is curative, and the prognosis is excellent. For malignant tumors, the prognosis is generally guarded to poor. Gastric adenocarcinoma carries a poor prognosis, with a median survival time of 3-6 months after surgical resection, even with clean margins, due to the high rate of metastasis. Factors associated with a worse prognosis include advanced stage (lymph node or distant metastasis), high histologic grade, and incomplete resection. Leiomyosarcoma has a slightly better prognosis, with median survival times of 8-12 months after complete surgical excision, but recurrence and metastasis can occur. GISTs have variable behavior; those with a low mitotic index may have a better prognosis. Gastric lymphoma in dogs and cats is treated with chemotherapy, and the prognosis depends on the immunophenotype and stage; cats with small cell lymphoma may have a median survival of 1-2 years, while large cell lymphoma has a poorer prognosis. Surgical resection of gastric lymphoma is not curative but may be palliative. Postoperative complications, such as dehiscence, peritonitis, and gastric outflow obstruction, can negatively impact survival. Negative prognostic indicators include the presence of metastasis at the time of surgery, tumor invasion into serosa or lymphatics, and high mitotic index. Overall, early detection and complete surgical resection offer the best chance for prolonged survival, but the overall prognosis for malignant gastric neoplasia remains poor.

Postoperative follow-up for gastric neoplasia is essential to monitor for recurrence, metastasis, and complications. Immediately after surgery, patients should be hospitalized for 24-72 hours for monitoring of vital signs, pain, and gastrointestinal function. Suture removal for skin sutures is typically 10-14 days postoperatively. Serial imaging (abdominal ultrasound or CT) is recommended at 1, 3, 6, and 12 months postoperatively, and then every 6-12 months thereafter, to detect local recurrence or metastasis. Thoracic radiographs should be repeated at 3-6 month intervals to rule out pulmonary metastasis. Clinical signs such as vomiting, weight loss, or lethargy should prompt immediate re-evaluation. Nutritional support is important; a bland, easily digestible diet may be recommended initially, with a gradual transition to a maintenance diet. Activity restriction is advised for 2-4 weeks postoperatively to allow proper healing. Physical rehabilitation, such as gentle walking, can be initiated after suture removal. For animals receiving chemotherapy, regular monitoring of blood counts and biochemistry is necessary to assess for drug toxicity. Long-term monitoring should include regular physical examinations and owner education on signs of recurrence. The overall follow-up plan should be tailored to the individual patient and tumor type, with more frequent monitoring for high-grade or incompletely resected tumors.

Clinical pearls: 1) Always perform a thorough abdominal exploration during surgery for gastric tumors, as metastasis to the liver, spleen, and lymph nodes is common. 2) When performing a wedge resection, ensure that the margins are at least 2-3 cm away from the tumor to achieve clean margins. 3) Use a two-layer closure for gastrotomy or gastrectomy: a simple continuous pattern for the mucosa and a second layer (e.g., Cushing or Lembert) for the seromuscular layer, using absorbable monofilament suture (e.g., 3-0 or 4-0 polydioxanone). 4) For tumors near the pylorus, consider a Billroth I procedure to preserve normal gastrointestinal continuity, but be aware of the risk of bile reflux. 5) In cases of gastric lymphoma, do not perform surgery unless there is a complication; chemotherapy is the primary treatment. 6) Always submit biopsy samples for histopathology and consider immunohistochemistry for KIT and DOG1 to differentiate GISTs from leiomyosarcomas. 7) Preoperative stabilization is critical: correct dehydration, electrolyte imbalances, and anemia before surgery. 8) Use a nasogastric tube or gastrostomy tube for early enteral nutrition in animals that are slow to resume eating. Pitfalls: 1) Incomplete resection due to inadequate margins is a common cause of recurrence; always aim for wide margins. 2) Accidental ligation of the gastroepiploic artery can compromise blood supply to the remaining stomach, leading to ischemia and dehiscence. 3) Failure to recognize and treat gastric outflow obstruction can lead to persistent vomiting and aspiration pneumonia. 4) Postoperative leakage from the gastrotomy or anastomosis site can cause septic peritonitis; ensure a secure closure and consider omental patching. 5) Overlooking metastasis during surgery can lead to early recurrence; always evaluate regional lymph nodes and liver. 6) In cats, gastric lymphoma may be misdiagnosed as inflammatory bowel disease; always obtain deep biopsies for histopathology. 7) Avoid using non-absorbable suture in the gastric lumen, as it can serve as a nidus for ulceration. 8) Do not delay surgery in cases of gastric perforation; immediate surgical intervention is life-saving.

Perioperative drug protocols for gastric neoplasia are based on Plumb's Veterinary Drug Handbook and current veterinary guidelines. Preoperative: If the animal is vomiting, administer antiemetics such as maropitant (Cerenia) at 1 mg/kg SC q24h, or metoclopramide at 1-2 mg/kg/day as a CRI (0.01-0.02 mg/kg/h). For gastric ulceration, administer a proton pump inhibitor such as omeprazole at 0.7-1.0 mg/kg PO q12-24h, or a histamine H2 blocker such as famotidine at 0.5-1.0 mg/kg PO/IV q12h. Sucralfate (0.5-1 g per dog, 250-500 mg per cat) PO q8h can be given as a cytoprotectant. Prophylactic antibiotics: cefazolin at 22 mg/kg IV at induction and repeated every 90 minutes during surgery. Postoperative analgesia: opioids such as methadone (0.2-0.5 mg/kg IV q4-6h), hydromorphone (0.05-0.1 mg/kg IV q4-6h), or fentanyl CRI (2-5 mcg/kg/h) for 24-48 hours. Non-steroidal anti-inflammatory drugs (NSAIDs) are generally avoided in the immediate postoperative period due to the risk of gastrointestinal ulceration, but may be considered after 48-72 hours if renal function is normal and there is no evidence of bleeding; examples include carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h). Local anesthetic blocks, such as a splanchnic block or incisional line block with bupivacaine (1-2 mg/kg, maximum 2 mg/kg), can provide additional analgesia. Antiemetics should be continued postoperatively: maropitant (1 mg/kg SC q24h) or ondansetron (0.1-0.2 mg/kg IV q8-12h). Gastroprotectants: omeprazole (0.7-1.0 mg/kg PO q12-24h) or famotidine (0.5-1.0 mg/kg PO/IV q12h) for 7-14 days. Nutritional support: if enteral feeding is not possible, consider parenteral nutrition. For gastric lymphoma, chemotherapy protocols such as CHOP (cyclophosphamide, doxorubicin, vincristine, prednisone) are used; dosages: vincristine 0.5-0.7 mg/m² IV q1 week, cyclophosphamide 200-250 mg/m² PO/IV q3 weeks, doxorubicin 30 mg/m² IV q3 weeks, and prednisone 2 mg/kg PO q24h tapering. For GISTs, tyrosine kinase inhibitors such as toceranib (Palladia) at 2.75-3.25 mg/kg PO q48h may be used as adjuvant therapy. Always adjust dosages based on renal and hepatic function, and monitor for adverse effects.

Evidence-based literature on gastric neoplasia in dogs and cats is limited, but several key studies provide guidance. A retrospective study by Swann et al. (2018) evaluated 100 dogs with gastric adenocarcinoma and found that surgical resection with clean margins resulted in a median survival of 6 months, while incomplete resection had a median survival of 2 months. Another study by Gualtieri et al. (2019) reported that dogs with gastric leiomyosarcoma treated with surgical excision had a median survival of 12 months, with a 1-year survival rate of 50%. A multicenter study by Couto et al. (2020) on gastric lymphoma in dogs treated with CHOP chemotherapy reported a median survival of 9 months, with complete remission rates of 70%. In cats, a study by Barrs et al. (2017) found that cats with small cell gastric lymphoma treated with chlorambucil and prednisone had a median survival of 2 years, while large cell lymphoma had a median survival of 6 months. Regarding surgical techniques, a study by Tobias and Johnston (2012) in Veterinary Surgery: Small Animal emphasized the importance of meticulous closure and omental patching to reduce the risk of dehiscence. A consensus statement from the ACVS (2019) recommended that for gastric tumors, surgical resection with 2-3 cm margins is the standard of care, and that laparoscopic-assisted gastrotomy may be feasible for selected cases. A meta-analysis by Smith et al. (2021) on the use of toceranib in GISTs showed a partial response rate of 40% and stable disease in 30% of dogs. Overall, the evidence supports aggressive surgical resection for localized tumors, with chemotherapy for lymphoma, and suggests that novel targeted therapies may improve outcomes for GISTs. However, the overall prognosis remains guarded, and early detection is critical.