The gastrointestinal tract consists of a tube that runs from the mouth to the anus. Its function is to digest food and absorb nutrients into the body. The stomach is a dilated part of the GI tract that produces acid, which helps with the initial breakdown of proteins. The small intestine extends from the stomach to the colon and serves to further breakdown food into absorbable nutrients. The cells lining the small intestine are distinctly different from that of the stomach.
Stomach tumors can be benign or cancerous (malignant), but most stomach tumors in dogs and cats are malignant with a high tendency to spread to other parts of the body. These tumors are more common in dogs than cats. If the cancer spreads, the liver and the lymph nodes are commonly affected; however, the cancer can also spread to the lungs. Lymphoma (commonly in the feline species), adenocarcinoma and leiomyosarcoma comprise the majority of malignant stomach tumors.
Benign tumors have also been reported and include extramedullary plasmacytoma and leiomyoma. Leiomyomas are easily treated with surgery and have a very good prognosis.
Signs and diagnosis
Certain breeds are more prone to develop stomach cancer: the rough collie, Staffordshire bull terrier, Belgian shepherd dog and chow chow. The median age of affected dogs is 9.5 years of age. The primary signs that the pet owner may see at home are vomiting, drooling, decreased activity, decreased appetite, black stools, abdominal pain and weight loss. Commonly, no additional signs are present upon physical examination by your companion’s veterinarian.
The diagnosis of a stomach tumor is made upon examination of the inside of the stomach with a flexible video camera called an endoscope. An X-ray following ingestion of barium contrast material is a less sensitive test used to identify a stomach tumor. Confirmation of the type of tumor requires a biopsy, which may be done at the time of endoscopic examination of the tumor, but is frequently done after the tumor has been removed. Tests done prior to surgery may include a complete blood count, blood chemistry profile and urinalysis to check internal organ health. Chest X-rays and abdominal ultrasound are used to identify visible spread of the cancer; however, microscopic spread of cancer to other organs cannot be detected with X-rays or ultrasound.
Surgery is recommended to remove a stomach tumor. Commonly, the tumor is located in the lower part of the stomach and a portion of the stomach will need to be removed along with a small portion of the small intestine. The remaining portion of the stomach is surgically reconnected to the small intestine (Bilroth type I procedure). While in the hospital, your companion will receive intravenous fluid therapy, intravenous antibiotic and sometimes anti-vomiting medication. Most patients remain in the hospital for two nights after surgery.
Chemotherapy is usually recommended if the tumor is malignant. This medication will be administered every two to three weeks via intravenous injection by an oncologist for a total of four to five treatments. The treatments are typically done on an outpatient basis and may take a total of 90 minutes to complete each visit. Unlike humans, most dogs do not lose their hair and usually have only mild side effects from the medication, which may include transient loss of appetite and vomiting.
The most common tumor, gastric adenocarcinoma carries a guarded prognosis, as over 70% of dogs have metastasis at the time of diagnosis. Overall survival times are commonly less than six months; however, in one study, the mean survival time was just over eight months (only 17 dogs had follow-up data). The average survival time following treatment of cats with gastric lymphoma with a Madison-Wisconsin chemotherapy protocol is ten months. Dogs with a gastric leiomyosarcoma can be potentially cured with surgery alone, but the literature for the most part indicates similar survival rates as gastric adenocarcinoma. Benign tumors also can be cured with surgical excision.
For more information on this subject, speak to the veterinarian who is treating your pet.