Dog Stomach Cancer Symptoms: What to Know

A stomach tumour can affect digestion, movement of food, appetite, and the stomach lining. A dog may vomit repeatedly, eat less, lose weight, seem tired, drool, show abdominal discomfort, or pass dark stools. Some digestive infections, ulcers, food intolerance, medicines, and other abdominal disorders can produce the same pattern. [Loss of Appetite](/symptoms/loss-of-appetite/) is a useful symptom to describe, not a diagnosis. The veterinarian will consider how long signs have lasted and whether they are worsening.

Arrange veterinary assessment when vomiting, appetite change, weight loss, or abdominal signs persist or recur. Bring a list of foods and medicines, a symptom timeline, and photographs of vomit or stool when safe to collect. Testing may include blood work, abdominal imaging, endoscopy, or tissue sampling. If stomach cancer is diagnosed, care may involve [Stomach Removal Surgery](/treatments/surgical-oncology/gastrectomy/), [Chemotherapy](/treatments/systemic-therapy/chemotherapy/), [HER2-Targeted Therapy](/treatments/systemic-therapy/her2-targeted-therapy/), or [Immunotherapy](/treatments/systemic-therapy/immunotherapy/), depending on the findings.

Seek urgent veterinary care for repeated vomiting with inability to keep water down, blood in vomit, black or tarry stool, a swollen painful abdomen, collapse, marked weakness, or breathing difficulty. These signs can signal bleeding, obstruction, dehydration, or another emergency.

Ask what causes are being considered, which test can distinguish them, and whether the stomach or another abdominal organ is involved. Ask how to support food and fluid intake, which changes require emergency care, and what treatment goals fit the dog’s condition.