Stomach Cancer in Dogs: Signs, Diagnosis, and Treatment

Name: Stomach Cancer in Dogs: Signs, Diagnosis, and Treatment
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-03

Stomach cancer in dogs is uncommon, but it is one of the more serious cancers a veterinarian can find. It usually causes long-lasting vomiting, appetite loss, and weight loss that do not improve with standard stomach treatments. Because those same signs show up with much more common problems, diagnosis takes several steps.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

The most common stomach cancer in dogs is gastric adenocarcinoma, which often forms near the pylorus (the outflow tract of the stomach) and can spread to lymph nodes, liver, and lungs [1].
Chronic vomiting, weight loss, a bloated or painful belly, and dark tarry stool are the signs owners notice most often [2].
Certain breeds carry a much higher risk, including the Belgian Tervueren, Belgian Groenendael, and Chow Chow [3][2][4].
Diagnosis usually requires blood work, imaging, and a stomach biopsy taken during endoscopy or surgery. Biopsy is the only way to confirm cancer.
Treatment depends on tumor type and stage. Surgery can cure some slow-growing tumors, while others are managed with chemotherapy and comfort care.

What Is Stomach Cancer in Dogs?

Stomach cancer means a malignant tumor growing from the tissues of the stomach wall. The most common type is gastric adenocarcinoma, a cancer of the glandular lining. In dogs, these tumors often form in the lower third of the stomach, near the lesser curvature and the pyloric region [1].

Other tumors can also arise in the stomach. Leiomyosarcoma, a cancer of smooth muscle, occurs most commonly in the stomach and small intestine, and gastrointestinal stromal tumors (GISTs) tend to grow in the cecum and large intestine [1]. Both GISTs and leiomyosarcomas usually grow slowly and spread slowly, with a reported metastatic rate of up to 30% in dogs [1]. That slower behavior matters, because it means some of these tumors can be removed successfully.

Gastric carcinoma itself is generally considered rare in dogs, and the outlook is grave for most cases [3]. The exception is a small number of breeds with a strong genetic risk, where the disease is far more common [3][4].

Signs of Dog Stomach Cancer

The signs of dog stomach cancer are easy to confuse with ordinary stomach upset at first. What sets cancer apart is that the signs keep going, they get worse, and they do not respond to usual treatments like diet changes or acid-reducing medication.

What owners notice first

Vomiting is the most common sign. In one review of 106 Chow Chows with gastric carcinoma, the most frequent clinical signs were vomiting, loss of appetite, diarrhea, and melena (black, tarry stool from digested blood) [2]. Signs began on average about 3 weeks before the diagnosis was confirmed [2].

Other signs owners report include:

Weight loss, sometimes rapid
A bloated or distended belly, or a belly that feels painful when touched
Drooling or lip smacking, which can signal nausea
Vomiting blood or material that looks like coffee grounds
Eating less or refusing food entirely
Low energy and hiding

A bloated belly with vomiting can also point to other serious problems, including fluid accumulation from liver disease. If your dog has a swollen abdomen along with yellow gums or eyes, see Canine Liver Disease: Symptoms, Diagnosis, Staging & Treatment. Vomiting that is yellow or bile-stained has its own list of causes, covered in Dog Vomiting Bile Cancer.

When vomiting is not stomach cancer

Most chronic vomiting in dogs is not cancer. Foreign bodies, chronic gastritis, inflammatory bowel disease, ulcers, parasites, and food intolerance are all far more common. A bleeding ulcer can cause vomiting and black stool that look identical to cancer signs, which is why testing matters. You can read more about that in Canine Gastric Ulceration: Diagnosis and Management.

Causes and Risk Factors

We do not know exactly what triggers most stomach cancers in dogs. What we do know is that genetics plays a large role in certain breeds.

Breeds at higher risk

The Belgian Shepherd varieties Tervueren and Groenendael have a well-recognized, high rate of gastric carcinoma [3][4]. In a Dutch birth cohort of dogs born between 2000 and 2010, the 10-year cumulative incidence was 4.7% for Tervueren and 2.1% for Groenendael, with no difference between males and females [4]. When at least one parent was affected, the odds of gastric carcinoma in the offspring were 5.0 times higher than when neither parent was known to be affected [4]. Mean age at diagnosis was about 8.5 years in Tervueren and about 10.1 years in Groenendael dogs [3].

The Chow Chow also carries an increased risk, confirmed through a large veterinary database review [2]. The tumors in these dogs look like the diffuse-type gastric carcinoma seen in human families, including signet ring and mucinous variants [2]. That similarity is one reason researchers study these breeds closely.

Age and other factors

Most dogs diagnosed with gastric carcinoma are middle-aged to older adults. Sex does not appear to affect risk in the Belgian Shepherd population [4]. Diet, environment, and lifestyle factors have not been clearly linked to stomach cancer in dogs, so no specific prevention advice can be given with confidence.

Polyps and precancerous changes

Gastric polyps in dogs rarely become malignant, but it can happen. One case report documented a gastric polyp in a Scottish Terrier that progressed over 14 months from a polyp to minimally invasive carcinoma to invasive adenocarcinoma, and the dog later developed widespread cancer spread including to the nervous system [5]. This is a single documented case, so the overall risk from polyps is still considered low [5].

How Veterinarians Diagnose Stomach Cancer in Dogs

Diagnosis is a step-by-step process. Your vet will first rule out common causes of chronic vomiting, then look for a mass.

Step 1: History and physical exam

Your vet will ask how long vomiting has been happening, what it looks like, whether your dog is eating, and whether stool color has changed. During the exam, they will feel the abdomen for a mass, thickening, or pain. A mass is not always palpable, especially early on.

Step 2: Blood work and stool testing

Blood work checks for anemia, electrolyte problems, and organ function. Some dogs with gastric tumors develop paraneoplastic syndromes, which are problems caused by the tumor itself instead of by direct spread. One case report described a dog with gastric adenocarcinoma that developed a syndrome of inappropriate antidiuretic hormone secretion, causing low sodium, low potassium, and low chloride levels that resolved after the tumor was removed [6]. Stool testing helps rule out parasites and other causes of diarrhea and black stool.

Step 3: Imaging

X-rays and ultrasound are the usual first imaging tests. Ultrasound can show thickening of the stomach wall and nearby lymph nodes. More advanced imaging, such as CT or PET/CT, can help locate the tumor and check for spread. In one case, 18F-FDG PET/CT was used to localize a gastric mass near the junction of the esophagus and stomach and to evaluate for metastasis before surgery [7].

Step 4: Biopsy

Biopsy is the gold standard for diagnosing gastric carcinoma [3]. Tissue is collected during endoscopy, which passes a camera and instruments through the mouth into the stomach, or during surgery. A pathologist examines the tissue and classifies the tumor type. Classification systems such as the WHO and Laurén methods are used in research settings, and in one study of 61 dogs with gastric carcinoma, the Laurén system split cases into 48% diffuse-type and 52% intestinal-type tumors [3].

Step 5: Staging

Staging means checking how far the cancer has spread. This matters because gastric and small intestinal adenocarcinomas frequently spread to regional lymph nodes, liver, and lungs [1]. At diagnosis, up to 32% of gastric adenocarcinomas and up to 77% of intestinal adenocarcinomas have already metastasized [1]. Staging tests are recommended whenever surgery is being considered [1].

Diagnostic step	What it looks for
Physical exam	Abdominal mass, pain, weight loss
Blood work	Anemia, electrolyte imbalances, organ function
X-rays and ultrasound	Stomach wall thickening, masses, lymph nodes
CT or PET/CT	Tumor location, spread to other organs
Endoscopy with biopsy	Confirms cancer type (gold standard)
Staging tests	Whether cancer has spread to liver, lungs, nodes

Treatment Options for Stomach Cancer in Dogs

Treatment depends on the tumor type, how far it has spread, and your dog's overall health. There is no single standard protocol that fits every dog.

Surgery

Surgery is the main treatment when the tumor can be removed. For tumors in the pyloric region, a procedure called a Billroth I can remove the affected part of the stomach and reconnect the remaining stomach to the intestine. In one case report, a dog with a pyloric gastric adenocarcinoma and severe electrolyte abnormalities had rapid resolution of those abnormalities after a Billroth I procedure and was still alive six months later with no recurrence [6].

Some slow-growing tumors have an excellent outcome after surgery. A 13-year-old Maltese dog with a gastric mass near the esophagogastric junction had the mass removed, and follow-up PET/CT six months later showed no recurrence or residual disease [7]. That tumor turned out to be a low-grade leiomyosarcoma, one of the slower-growing types [7].

Chemotherapy

Chemotherapy is used when cancer has spread, when surgery cannot remove everything, or as a follow-up to surgery. In the Chow Chow review, two dogs treated aggressively with both surgery and chemotherapy survived 12 and 36 months, far longer than the typical outcome [2]. Most dogs in that group were euthanized without treatment within 2 weeks of diagnosis [2], which shows how much treatment choices can affect survival time.

Supportive and comfort care

Supportive care focuses on quality of life. Options include anti-nausea medication, appetite stimulants, pain control, and intravenous fluids for dehydration. Your veterinarian will calculate every dose based on your dog's weight and health status. Feeding tubes or special diets may help dogs who will not eat.

What to expect from prognosis

The general outlook for gastric adenocarcinoma is poor, even with surgery and medical treatment [1]. Many gastrointestinal neoplasms in dogs are biologically aggressive, and intensive treatment is often needed just to improve the patient's clinical status [1]. Some cancers, such as colorectal adenocarcinoma and lymphoma, carry a more favorable prognosis with extensive treatment [1]. Your vet will give you a realistic picture based on your dog's specific tumor type and stage.

Recovery, Outlook, and Long-Term Management

If your dog has surgery, expect a hospital stay and a recovery period with restricted activity and small, frequent meals. Your vet will schedule rechecks to monitor healing and watch for recurrence. Follow-up imaging may be recommended, as it was in the Maltese dog that had repeat PET/CT six months after surgery [7].

If your dog is not a surgical candidate, management centers on comfort. Track good days and bad days. Note whether your dog still enjoys food, walks, and time with you. Your vet can adjust medications as needs change.

Long-term monitoring usually includes periodic blood work and imaging. There is no widely accepted blood test that reliably detects recurrence of stomach cancer in dogs, so imaging and clinical signs remain the main tools.

Prevention

There is no proven way to prevent stomach cancer in dogs. Because genetics plays such a strong role in certain breeds, the most meaningful step is informed breeding. The heritability findings in Belgian Shepherds support using parent disease status in breeding decisions to reduce risk in future generations [4].

For owners, the practical steps are:

Know your breed's risk. If you have a Belgian Tervueren, Groenendael, or Chow Chow, mention it to your vet at every wellness visit [3][2][4].
Do not ignore chronic vomiting. Vomiting that lasts more than a few days, or that comes with weight loss, deserves a workup.
Keep regular wellness exams, especially as your dog enters middle age and beyond.
Report black or tarry stool right away, since it can signal bleeding in the stomach.

Limitations and When to Contact a Veterinarian

Stomach cancer cannot be diagnosed from signs alone. Many conditions cause the same symptoms, and only testing can tell them apart. Every case needs a veterinarian who can examine your dog, review the history, and order the right tests.

Contact your veterinarian the same day if your dog:

Vomits repeatedly and cannot keep water down
Has a belly that looks swollen or feels painful
Passes black, tarry stool or vomits blood
Refuses food for more than 24 hours
Seems weak, wobbly, or unusually quiet

Go to an emergency clinic now if your dog:

Collapses or cannot stand
Has a hard, distended abdomen that is painful to touch
Is vomiting large amounts of blood
Is struggling to breathe

Call for a routine visit if your dog:

Has vomited on and off for more than a week
Is slowly losing weight
Has a change in appetite or stool consistency that persists

Frequently Asked Questions

How common is stomach cancer in dogs?

Gastric carcinoma is generally considered rare in dogs, though it is much more common in a few breeds with strong genetic risk [3]. The 10-year cumulative incidence in Belgian Tervueren dogs was 4.7% and in Groenendael dogs was 2.1% [4]. For most other breeds, the disease is uncommon.

Can stomach cancer in dogs be cured?

Sometimes. Slow-growing tumors such as low-grade leiomyosarcoma and gastrointestinal stromal tumors can be removed surgically with good outcomes, and one dog remained free of recurrence six months after surgery [7]. Aggressive adenocarcinomas are much harder to cure, and the overall prognosis is poor even with treatment [1].

How long can a dog live with stomach cancer?

It varies widely. In one breed review, most affected dogs were euthanized within 2 weeks of diagnosis, but two dogs treated with surgery and chemotherapy survived 12 and 36 months [2]. Survival depends on tumor type, stage, treatment chosen, and your dog's overall health.

Does a bloated belly always mean stomach cancer?

No. A bloated belly has many causes, including fluid buildup, gas, and other organ disease. Stomach cancer is one possibility among many. Only a veterinary exam and testing can determine the cause.

Are stomach tumors in dogs always malignant?

No. Some growths in the stomach are benign, and gastric polyps in dogs rarely become malignant [5]. However, malignant transformation of a polyp has been documented, so any stomach mass should be evaluated by a veterinarian [5].

References

Gastrointestinal Neoplasia in Dogs and Cats - Digestive System. Merck Veterinary Manual.
Risk and characteristics of gastric carcinoma in the chow chow dog. The Canadian veterinary journal = La revue veterinaire canadienne, 2020.
The Histopathological Characteristic of Gastric Carcinoma in the Belgian Tervueren and Groenendael Dog: A Comparison of Two Classification Methods. Animals : an open access journal from MDPI, 2023.
Incidence and Heritability of Gastric Carcinoma in the Belgian Shepherd Dog Population in The Netherlands. Veterinary sciences, 2025.
Malignant transformation and subsequent leptomeningeal carcinomatosis of a gastric polyp in a dog. Journal of veterinary internal medicine, 2024.
Suspected paraneoplastic syndrome of inappropriate antidiuretic hormone secretion associated with a gastric adenocarcinoma in a dog. Australian veterinary journal, 2024.
Use of 18-Fluorodeoxyglucose Positron Emission Tomography and Near-Infrared Fluorescence-Guided Imaging Surgery in the Treatment of a Gastric Tumor in a Dog. Animals : an open access journal from MDPI, 2024.