Stomach cancer in dogs usually refers to a malignant type of cancer that tends to spread (metastasis) to other organs. It is often diagnosed late in its stages which may lead to a poor prognosis. Not all stomach cancers in dogs though are created equally. There are several types of stomach cancer in dogs and proper diagnosis requires several tests to determine exactly what type is present. Following are several types of stomach cancer in dogs along with some detailed information about how common they are, therapy options and overall prognosis .
Types of Stomach Cancer in Dogs
Stomach cancer in dogs, medically referred to as gastric cancer, tends to affect several dogs, but there is a predilection for middle-aged and older dogs. The average age of affected dogs is roughly 8 years, with males dogs generally affected more than females.
It's important to rule out stomach cancer in dogs (especially older dogs) with a history of having excess salivation, bad breath, chronic vomiting, presence of blood in vomit, pale gums, loss of appetite, lethargy and weight loss. The weight loss may be due to chronic vomiting, loss of protein and blood from ulcers, poor digestion or cancer cachexia.
Symptoms of stomach cancer in dogs may go on for several weeks to many months ( from less than four months or less to as much as 18 months). The earlier the diagnosis the better, considering that, as already mentioned, this condition is often discovered too late when the prognosis becomes poor and treatment options are limited.
It is unfortunate that often dogs tend to hide signs of stomach pain and discomfort which puts a dent in discovering this condition at its earliest stages. On top of that, not all dogs with early stomach cancer will necessarily vomit other than perhaps intermittently. It's unfortunate that the symptoms tend to become more evident only once the cancer spreads and starts affecting more parts of the stomach.
Did you know? Although worrisome, gastric tumors are quite uncommon and comprise less than 1 percent of all neoplasms found in cats and dogs.
At the Vet's Office
Diagnosis of stomach cancer in dogs is obtained by running several tests that help rule out other medical conditions and confirm stomach cancer. The vet may run blood tests, fecal exams and x-rays.
Blood tests often encompass a complete blood count and biochemistry profile. These tests can help rule out other common causes for vomiting such as liver and kidney disease and adrenal gland disease. The presence of microcytic hypochromic anemia ( low red blood cells that are both smaller and paler than normal) may be suggestive of stomach cancer once other potential causes are ruled out. Elevation of liver enzymes instead can be indicative of cancer spread to the liver or bile duct obstruction.
Fecal tests may help rule out parasites and protozoans. The presence of occult blood can be suggestive of stomach cancer (due to bleeding stomach ulcers) once other potential causes are ruled out. X-rays are generally not diagnostic for stomach cancer in dogs, however they may reveal abnormalities such as thickened stomach wall or displacement of the stomach, and in some cases, chest x-rays may also show signs of spread of the cancer to the lungs. X-rays can too help rule out presence of foreign bodies. Double contrast barium radiography and fluoroscopy may be more insightful revealing presence of masses, ulcers, delayed gastric emptying or poor motility.
An ultrasound, although costly, may evaluate stomach wall changes, detect presence of enlarged lymph nodes and possible stomach tumors, while helping rule out out other causes of vomiting (pancreatitis, liver disease, etc). It is only through a biopsy though that the vet can determine whether the tumors are benign or malignant. Needle biopsies may be obtained during an ultrasound which may be evaluated for lymphosarcoma, and occasionally, adenocarcinoma.
The best way to obtain biopsies is through an endoscopy, a procedure where a thin tube is inserted down the dog's throat into the stomach and several tissue samples are collected. Even better biopsy samples though may be obtained surgically as it may happen to dogs undergoing exploratory surgeryat that time.
As mentioned, not all stomach cancers in dogs are the same. Following is a list of some common and less common types of stomach cancer in dogs.
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Among all the different types of stomach cancers in dogs, gastric adenocarcinomas (ACA) rank as the most common. According to Clinical Veterinary Oncology, gastric adenocarcinoma accounts for 60 to 70 percent of all cancers of the stomach.
This type of cancer is mainly found in older dogs and is mostly located in the lower ⅓ of the stomach affecting the stomachs' antrum and pyloric areas. Some breeds appear to be affected more than others, particularly rough collies, Staffordshire terriers, Belgian shepherds, and chow chows.
This type of cancer has a tendency to be aggressive and frequently spreads to the dog's regional lymph nodes (in about 50 to 60 percent of cases) or to the dog's liver, spleen, omentum and lungs. It is estimated that at the time of diagnosis, as many as 95 percent of gastric adenocarcinomas have already spread.
Surgery is the most common form of treatment, especially in cases where there are no signs of the cancer spreading. "The average life expectancy after surgery for this type of tumor is probably only six months to a year, but dogs do seem to be comfortable most of that time," says Johnny D. Hoskins, a board-certified veterinarian specializing in internal medicine. However surgery is not without any challenges especially considering the difficulties in removing an advanced cancer from a debilitated dog.
Some cancers may be very extensive and things may be too advanced to make this type of surgery worthy. Surgery may provide palliative effect in case of stomach obstructions. Unfortunately, radiation therapy or chemo are not very successful in granting much long-term survival for this form of cancer. Consultation with an oncologist is recommended.
"Gastric adenocarcinoma carries a poor to grave prognosis. Most patients have extensive local disease or metastasis at the time of diagnosis."~Dr. Rance K. Sellon
Leiomyosarcoma (LMS) is a less metastatic form of cancer (30 percent are expected to spread) compared to adenocarcinoma. This is a smooth muscle tumor which tends to occur infrequently and is typically slow to metastasize. Leiomyosarcomas tend to form in the stomach and small intestine. This is the second most common gastric tumour found in dogs. (Kapatkin et al 1992, Swann & Holt 2002)..
A positive feature for this type of cancer is that, when it has not spread to the liver, it is possible to surgically remove, and affected dogs may have a good prognosis with affected patients potentially living for a year or more following surgery.
Affected dogs in the early stages may show hypoglycemia (low blood glucose values) in blood tests and may develop polyuria and polydipsia (increased urination, increased drinking).
Dogs affected by this type of tumor generally have a good prognosis as long as the tumor is removed entirely and there is no evidence of the cancer spreading.
Other Types of Stomach Cancer in Dogs
Following adenocarcinoma and leiomyosarcoma, the third most common type of stomach cancer in dogs is malignant lymphoma. Other types of gastric cancer in dogs include gastrointestinal stromal tumor (GIST), scirrhous carcinoma and histiocytic sarcoma.
Rare stomach tumors include extramedullary plasmacytoma, mast cell tumour, fibrosarcoma, adenomatous polyp, gastric lymphoma (not to be confused with confused with lymphoma cancer ), squamous cell carcinoma, fibroma, and carcinoid tumours of the enterochromaffin cells.
Benign Types of Stomach Cancer in Dogs
For those wondering, not all stomach cancer in dogs are necessarily malignant. There are also benign types of stomach cancer in dogs and these include leiomyomas, adenomas, hyperplastic polyps and hypertrophic gastropathy. Dogs with leiomyomas, in particular are usually quite old (average, 16 years old). Dogs with benign lesions can be fortunately cured with surgical removal of the mass.
- Kapatkin AS, Mullen HS, Mathiesen DT, et al. Leiomyosarcoma in dogs: 44 cases (1983–1988). J Am Vet Med Assoc 1992;201:1077–1079
- Withrow SJ, MacEwen G. Small Animal Clinical Oncology, 3rd ed. Philadelphia, PA: WB Saunders; 2001:336
- DVM360: Gastric neoplasms in dogs and cats (Proceedings)
- DVM360: Gastric neoplasia best treated surgically
- Tumors of the Abdominal Cavity Leslie E. Fox, Jeffrey N. Bryan, in Cancer Management in Small Animal Practice, 2010