You're smart to to have the endoscopic biopsy performed because there are quite a few possibilities for that mass. While a malignancy is most likely in an 11 year old, you'll see in the synopsis I'm going to post below that there are benign and curable neoplasms as well. This synopsis is from Clinical Veterinary Advisor, 3rd Ed., Cote', 2015:
- Median age for adenocarcinoma is 10 years.
- Median age for leiomyomas is 11 years.
Genetics and Breed Predisposition
- Chronic nitrosamine exposure experimentally
- Association of gastric carcinoma and lymphoma with chronic inflammation from Helicobacter pylori infection in people; suspected in companion animals
Contagion and Zoonosis
- Helicobacter spp. organisms are often found in normal dogs and cats, but are of unknown pathologic significance.
- Zoonotic potential exists for H. pylori, but prevalence in animals is low. (In summary, a bacterial infection shouldn't be a consideration for him.)
History, Chief Complaint
- Chronic vomiting
- Anorexia, weight loss
- Depression and lethargy, signs of pain or restlessness
Physical Exam Findings
May include some or all of the following:
- Physical exam may be normal
- Poor body condition score (e.g., body condition score 1/9-2/9)
- Pale mucous membranes, signs of anemia
- Abdominal mass
- Abdominal pain
Etiology and Pathophysiology
- Chronic vomiting may result in weight loss, electrolyte imbalance.
- Anemia secondary to chronic GI bleeding may be hypochromic, microcytic due to iron depletion.
- Panhypoproteinemia due to GI blood loss
- Hypoglycemia may occur secondary to insulin-like growth factor II release from smooth muscle tumors.
- GISTs are associated with activating mutation of the c-kit receptor tyrosine kinase oncogene.
The diagnosis is suspected when nonspecific signs of GI disturbance fail to respond to conservative management and/or are accompanied by systemic changes (e.g., weight loss). Radiographs and ultrasound may help to localize the lesion; confirmation requires a biopsy for histopathologic evaluation.
Any GI or systemic cause of chronic vomiting may mimic gastric neoplasia:
- Gastric foreign body
- Gastric ulceration
- Granulomatous gastritis
- Chronic pancreatitis
- Systemic disease associated with chronic vomiting (renal, hepatic, diabetic ketoacidosis)
- CBC, serum chemistry panel with electrolytes, urinalysis: frequently normal, or changes are nonspecific and secondary to GI electrolyte or blood losses (nonregenerative anemia, increased blood urea nitrogen, normal creatinine, normal urine specific gravity)
- Three-view thoracic staging radiographs (metastasis)
- Abdominal ultrasound evaluation: to assess gastric wall changes often not seen on routine radiographs and to rule out other causes of vomiting (pancreatitis, liver disease, etc.)
- Positive contrast gastrogram: assessment for outflow obstruction; does not differentiate neoplasia from other infiltrative diseases such as pythiosis
- Ultrasound-guided fine-needle aspiration and cytologic evaluation: if a gastric wall abnormality or lymphadenopathy is present. Lymphoma exfoliates most readily; GIST or gastric muscle tumors do not.
- Endoscopic biopsy: histopathologic diagnosis is essential for treatment and prognosis. Endoscopy effectively provides mucosal tissue specimens, but if the tumor is in the gastric muscular or serosal layers, results may be inadequate, requiring surgical biopsy.
- Surgical biopsy: exploratory surgery provides opportunity for both diagnosis and treatment (surgical removal of the affected region).
Advanced or Confirmatory Testing
Diagnosis is confirmed histopathologically and can be further refined through the application of advanced techniques:
- Immunohistochemical stains for c-kit in GIST
- Cytokeratin, vimentin immunohistochemistry for undifferentiated tumors
- Immunophenotyping for lymphoma
Benign gastric lesions can be cured surgically, as can early-diagnosed, low-grade malignancy. Other surgical goals are to relieve gastric obstruction or remove tumors for clinical palliation. Chemotherapy is potentially helpful in prolonging survival, although malignant gastric tumors are typically incurable. Consultation with/referral to an oncologist is recommended.
Acute General Treatment
- Antiemetics (maropitant 1 mg/kg PO, SQ; or dolasetron 0.3 mg/kg q 12-24h IV, SQ; or metoclopramide 0.2-0.4 mg/kg q 8h PO or IV, if no obstruction present), gastroprotectants (famotidine 0.5 mg/kg IV, PO q 12h; or omeprazole 1 mg/kg PO q 24h)
- Fluid resuscitation/rehydration with intravenous fluids
- Antibiotics for Helicobacter infection if indicated
- Blood transfusion (see p. 1233) and hematinic therapy for nonregenerative iron-deficiency anemia
- Analgesic management as indicated by clinical signs
- Diet modification to easily digested, high-energy content food
- Parenteral alimentation as indicated (if the patient has not eaten for > 3 days or will not be able or willing to eat after surgery; see p. 1213)
- Gastric tumor resection often results in motility disorders.
- May require motility modifiers (metoclopramide 0.2-0.4 mg/kg IV, PO q 8h; or cisapride 0.25 mg/kg PO q 24h)
- Chronic antiemetic therapy may be required.
- Chemotherapy with doxorubicin, platinum agents, or antimetabolites may prove helpful, depending on tumor type.
- Systemic chemotherapy for gastric lymphoma provides remission and prolonged survival (see p. 621).
- Receptor tyrosine kinase inhibitor for GIST with kit gene mutation (toceranib 2.5-3.25 mg/kg PO q 24h, 48h or M,W,F; masitinib 12.5 mg/kg PO q 24h)
- Surgical wound dehiscence with secondary peritonitis, pneumoperitoneum
- Chemotherapy-induced leukopenia might predispose to infection.
- Chemotherapy-induced thrombocytopenia might increase gastric hemorrhage.
- Chemotherapy might result in perforation of transmural lesions.
- Postoperative follow-up with chest radiographs and abdominal ultrasound for signs of recurrence or metastasis on a 1- to 2-month basis for 1 year
- Monitor CBC for recovery from nonregenerative anemia.
- Monitor for signs of dissemination of alimentary lymphoma.
Prognosis & Outcome
- Favorable for benign lesions (adenomas, leiomyomas), although complete resection of mesenchymal tumors is unlikely
- Poor for adenocarcinoma, carcinoma, GIST, especially when metastatic:
- These dogs generally do not live beyond 6 months, even with therapy.
- Guarded to fair for focal mass presentation of lymphoma
- Guarded for diffuse or multicentric alimentary lymphoma, as these lesions typically regress slowly and may have an indolent course but are ultimately incurable
Pearls & Considerations
- Gastric carcinoma is associated with early lymphatic spread. Lymph nodes detected on ultrasound can be used for diagnosis and prognosis.
- Gastric carcinomas may overexpress cyclooxygenase-2; nonsteroidal antiinflammatory drugs (piroxicam 0.3 mg/kg PO q 24h) may be palliative, but careful monitoring for adverse GI effects of such drugs is important.
- Scirrhous carcinoma is rapidly fatal.
Please respond with further questions or concerns if you wish.