Gastrointestinal (GI) Neoplasia in Dogs

Overview of Canine Gastrointestinal Cancer

Gastrointestinal neoplasia is cancer located anywhere throughout the gastrointestinal (GI) tract, including the oral cavity (mouth), esophagus, stomach, small intestines, large intestines and rectum. GI cancer can be primary, which means it originates in the GI tract, or metastatic, which is spread from another site.

No specific causes of primary cancer have been identified, although it has been associated with several disorders. Chronic inflammation or irritation has been thought to be a contributing factor in some cases. Spirocerca lupi, a parasite of the esophagus, may cause associated cancer.

Cancer usually occurs in middle-aged to older dogs. Depending on the tumor type and location, different breeds, ages, and species can be affected. The Belgian shepherd and Scottish terrier have a higher incidence of gastric carcinoma than other breeds. Collies are also more likely to develop malignant intestinal cancer.

What to Watch For

With gastrointestinal cancer, clinical signs are largely dependent on the location of the cancer, size of the mass, and to a degree, the specific type of cancer. General signs to watch for by location include:

• Oral. Watch for halitosis (bad breath), bleeding from the mouth, difficulty eating and drooling.
• Esophageal. Watch for regurgitation, excessive salivation and weight loss.
• Gastric (stomach). Watch for vomiting (with or without blood), weight loss, inappetence and black tarry feces.
• Small intestinal. Watch for diarrhea, vomiting, weight loss, anorexia, black, tarry feces and gas.
• Colonic (large intestinal). Watch for diarrhea (with mucus or blood) and straining to defecate.
• Rectal. Watch for straining and blood in stool.

Diagnosis of Gastrointestinal Neoplasia in Dogs

Your veterinarian may recommend the following diagnostic tests:

• Baseline tests to include a complete blood count (CBC), biochemical profile and urinalysis
• Fecal examination
• Abdominal radiographs (x-rays)
• Thoracic (chest) radiographs
• Abdominal ultrasound
• Upper gastrointestinal contrast radiography (dye study)
• Endoscopy of the upper and/or lower bowel and biopsy
• Abdominal exploratory and biopsy

Treatment of Gastrointestinal Neoplasia in Dogs

• Hospitalization and support as needed, such as fluid therapy or blood transfusions
• Surgical resection (removal), which is the treatment of choice
• Surgical debulking (removing as much as possible) to help improve clinical signs
• Chemotherapy
• Radiation therapy
• Dietary manipulation

Home Care

Administer medication and diet as directed by your veterinarian. Return for follow-up as directed by your veterinarian. If your pet has a recurrence of signs, contact your veterinarian at once.

Prognosis varies depending on the location, size, type and ability to remove the tumor surgically.

There is no known specific prevention of gastrointestinal cancer. Treat all underlying inflammatory disorders in their early stages if possible.

In-depth Information on Gastrointestinal Neoplasia in Dogs

Gastrointestinal (GI) neoplasia (cancer) occurs infrequently in dogs as compared to neoplasia involving other systems. Over two-thirds of GI neoplasms in dogs are malignant – they are aggressive, and often spread locally or to other areas. The most common types of gastrointestinal tumors include adenocarcinoma, lymphoma, leiomyosarcoma, leiomyoma, squamous cell carcinoma, fibrosarcoma, plasmacytoma, and mast cell tumors. In general, older animals are affected most commonly.

The cause of GI neoplasia is rarely evident, and signs can be extremely variable from patient to patient as signs usually reflect the size, location, and type of tumor. Some patients may be relatively asymptomatic, while others may be in immediate need of intensive support and hospitalization, to include intravenous fluid therapy and blood transfusions. There are many diseases/disorders that cause similar clinical signs to patients with gastrointestinal neoplasia.

Esophageal Neoplasia

Esophageal cancer is the least common site for tumors in the GI tract. The most common tumors associated with the esophagus include squamous cell carcinoma, fibrosarcoma, and sarcoma (associated with the parasite Spirocerca lupi).

Megaesophagus, which is a distended and/or poorly functional esophagus, and as the clinical signs seen with this condition (regurgitation, excessive salivation, and difficulty eating/swallowing) often mimic esophageal neoplasia, it needs to be considered and differentiated.

There are many diseases associated with megaesophagus:

• Intrathoracic masses/growths may put pressure on the esophagus from the outside, creating a blockage
• Vascular ring anomaly is an entrapment of the esophagus within several structures, causing a partial megaesophagus
• Neuromuscular diseases (nerve and muscle) including myasthenia gravis, polymyositis, systemic lupus erythematosus, polyradiculoneuritis, botulism, tetanus and dysautonomia
• Central nervous system diseases including infectious, inflammatory, neoplastic (cancerous) and traumatic disorders
• Miscellaneous disorders including endocrine diseases (hypothyroidism, hypoadrenocorticism), certain toxicities (lead, thallium, acetycholinesterase), and thymomas, which are tumors arising from an organ in the chest
• Esophagitis is the inflammation of the esophagus and needs to be differentiated
• Esophageal foreign body is an object within the esophagus and have symptoms similar to esophageal neoplasia
• Esophageal stricture is an abnormal narrowing of the esophagus and should be ruled out
• Esophageal diverticula are pouch-like dilatations of the esophageal wall and should be ruled out
• Esophageal fistula is an abnormal communication between the esophagus and another structure
• Hiatal hernia is an abnormality of the diaphragm allowing part of the stomach to be displaced into the chest cavity and needs to be ruled out

Gastric and Small Intestinal Neoplasia

Adenocarcinoma is the most common gastric and small intestinal tumor of dogs. In general, the most common tumors seen in the stomach and small intestines of dogs are adenocarcinoma, lymphosarcoma, leiomyosarcoma, leiomyomas, fibrosarcoma, squamous cell carcinoma, plasmacytoma, and mast cell tumors.

Many diseases/disorders cause similar clinical signs to patients with gastric and small intestinal neoplasia such as vomiting (with or without blood), diarrhea, melena (dark, tarry feces), inappetence and weight loss, and should be considered and differentiated.

• The ingestion of certain drugs may cause gastrointestinal ulceration, vomiting (with or without blood), and inappetence.
• Metabolic disorders (kidney failure, liver disease, hypoadrenocorticism) are often associated with GI signs.
• Stress, pain, fear and/or major medical illness to include shock, hypotension (low blood pressure), trauma, and major surgery can all be associated with gastrointestinal signs.
• Dietary indiscretion (ingestion of garbage) is a common disorder seen in both cats and dogs. Vomiting and diarrhea are commonly seen.
• Pancreatitis is an inflammation of the pancreas, and in certain cases, can be life-threatening. The most common clinical signs seen with pancreatitis are vomiting and inappetence.
• Intestinal obstruction/blockage secondary to foreign bodies must be differentiated from GI tumors.
• Mast cell tumors, cancer of the liver, and gastrin secreting tumors of the pancreas should be considered.
• Infiltrative diseases, which are microscopic diseases that penetrate and spread, of the gastrointestinal tract (inflammatory bowel disease) must be ruled out.
• Hemorrhagic gastroenteritis is a syndrome seen in dogs whose cause is unknown. These animals often have vomiting (with or without blood) and bloody diarrhea. Hemorrhagic gastroenteritis is most often seen in urban settings in small breed dogs.
• Clotting disorders, such as thrombocytopenia (decreased platelet count) or warfarin toxicity (rat poison), may present with melena (dark, tarry feces), bloody diarrhea or vomiting.
• Certain toxins (such as lead) can cause severe gastrointestinal signs.

Large Intestinal and Rectal Neoplasia

Adenocarcinoma is the most common tumor of the colon in dogs. The most common tumors of the colon/rectum in general are adenocarcinoma, lymphosarcoma and plasmacytoma. There are many diseases/disorders that cause similar clinical signs to patients with large intestinal and rectal neoplasia including tenesmus (straining to defecate) and hematochezia (blood in the stool), and should be considered and differentiated.

Colonic/rectal disorders include:

• Infectious agents (bacterial, viral, or parasitic) often cause blood and/or mucus in the feces
• Constipation causes tenesmus (straining to defecate) and needs to be differentiated from colo-rectal cancer
• Colitis/proctitis (inflammation of the colon/rectum) commonly presents for straining and blood in the stool
• Foreign bodies of the colon and rectum can mimic neoplasia
• Strictures (narrowing) of the colon or rectum often cause straining and blood

Perineal/perianal (around the anus) disorders include:

• Anal sac abscesses or neoplasia cause blood in the stool and straining
• Perineal hernia is a laxity in the muscle tissue that surrounds the anus internally, causing an outpouching and associated straining to defecate
• Perianal fistula (ulcerations or tracts present around the anus) may cause pain, blood and straining associated with defecation
• Pseudocoprostasis (hair around the anus becomes matted with feces) may be associated with straining

Miscellaneous Disorders

• Abdominal cavity masses/growths of any organ can compromise areas of the intestinal tract and cause associated signs.
• Pelvic masses or fractures can cause difficulty defecating.
• Prostatic disorders (hypertrophy/enlargement, neoplasia, prostatitis/inflammation, abscess) are often associated with straining.

In-depth Information on Diagnosis

A diagnosis of gastrointestinal neoplasia in dogs can be made more easily in some cases than in others. A full diagnostic work up is recommended. A definitive diagnosis can only be made with the evaluation of tissue; therefore, a biopsy is necessary for a bottom line diagnosis of GI neoplasia and specific tumor type.

• A complete blood count (CBC) will evaluate for the presence of infection, inflammation, and anemia, sometimes associated with gastrointestinal neoplasia.
• A biochemical profile evaluates the kidney, liver, electrolytes, total protein, and blood sugar status. All of these parameters are important to establish in the patient with gastrointestinal neoplasia, as these changes can be seen associated with other disorders as well.
• A urinalysis helps evaluate the kidneys and hydration status of the patient.
• Multiple fecal examinations are important to rule out gastrointestinal parasites as a cause of vomiting, diarrhea, or other gastrointestinal signs.
• Abdominal radiographs (X-rays) evaluate the abdominal organs (kidneys, liver) and may help visualize the presence of a foreign body or tumor.
• An abdominal ultrasound evaluates the abdominal organs and helps assess for the presence of tumors. Organs, lymph nodes, and masses can be sampled with a needle or biopsy instrument with the guidance of ultrasound. This procedure is relatively safe, however may necessitate a sedative. It is often recommended that a specialist perform the procedure.
• Thoracic (chest) radiographs should be obtained to evaluate esophagus and to assess for the presence of metastatic disease (spread of cancer to the chest).

Your veterinarian may recommend additional tests to insure optimal medical care. These are selected on a case-by-case basis.

• A coagulogram (clotting profile) may be recommended in cases of GI bleeding to rule out associated thrombocytopenia (decreased platelets) or clotting factor abnormalities.
• An ACTH stimulation test may be recommended to rule out hypoadrenocorticism (Addison’s disease), which can cause gastrointestinal signs. It is a combination of two blood tests that measures adrenal function. It is safe, and can usually be performed at your local veterinary hospital.
• Bile acids are paired blood tests obtained before and after a meal that evaluates liver function, as certain liver diseases can be associated with GI signs. The test is very safe and can be performed at your local veterinary hospital.
• A blood lead level should be performed in patients where there has been known or possible lead exposure.
• A gastrin level should be run on any patient with multiple or recurrent ulcers. Elevated levels are usually seen in patients with gastrinomas, which are tumors that secrete gastrin, increasing stomach acid production and causing ulceration.
• An upper gastrointestinal (GI) barium (dye) series may be helpful in identifying tumors. A safe dye is given to the patient by mouth, and is then watched as it travels through the GI tract. It is a non-invasive test that can often be performed by your regular veterinarian, although in some cases may necessitate transfer to a specialty hospital.
• A reticulocyte count should be performed on anemic animals. This will help determine if the type of anemia is consistent with gastrointestinal bleeding (secondary to a tumor) or some other cause.
• A bone marrow aspirate may be recommended in some patients with anemia, to determine if it is secondary to a GI bleed or a primary problem in the bone marrow (associated cancer/lymphosarcoma). It is a relatively noninvasive test. It allows us to sample the marrow (substance inside of the bone), which is responsible for producing red blood cells, white blood cells and platelets. With a local anesthetic, a small needle is introduced into the core of the bone, and a small amount of marrow is withdrawn and analyzed. This test may be performed by your local veterinarian, although in some cases, may be best to have performed in a specialty hospital.
• Gastroduodenoscopy (upper GI endoscopy) or colonoscopy (large bowel endoscopy) may be of benefit. It may help evaluate these areas for growths, and sample tissue for the presence of inflammation or cancer. Hospitalization is brief, and healing is generally quick and uneventful. It does, however, necessitate general anesthesia, and therefore is associated with minor risks.
• Lastly, an exploratory laparotomy should be performed as a diagnostic (and sometimes therapeutic) tool in any individual that has had an extensive diagnostic and sometimes therapeutic (treatment) course, with little or no response. It is an invasive procedure, however is necessary in a handful of cases for a definitive diagnosis.

In-depth Information on Therapy

Treatment of gastrointestinal neoplasia in dogs largely depends on surgical excision. If complete excision of the primary tumor is impossible, or metastasis has occurred, other therapy can be attempted. These treatments may reduce severity of symptoms or provide relief for your pet.

• Fluid and electrolyte therapy may be necessary in some patients with gastrointestinal neoplasia, and is directed toward correcting dehydration, acid-base, and electrolyte abnormalities. Additionally, blood transfusions may be indicated in the severely anemic patients who have bleeding tumors.
• Depending on the location of the neoplasia, dietary recommendations may vary. Patients with esophageal tumors may benefit from a gruel or canned food. Those with gastric or intestinal lymphoma may benefit from small, frequent feedings. Parenteral (intravenous) nutrition or feeding tubes may be of benefit in certain cases.
• Drugs that decrease or inhibit acid production by the stomach such as Tagamet® (cimetidine), Pepcid® (famotidine), Zantac® (ranitidine), Cytotec® (misoprostol) and Prilosec® (omeprazole) encourage and expedite the resolution of GI inflammation, especially esophagitis and severe gastritis from excessive vomiting, often associated with GI neoplasia.
• Gastrointestinal protectants and adsorbents (medications that protect or sooth) are felt to coat an “irritated” GI lining and bind “noxious” (harmful) agents, and may offer symptomatic relief to patients with upper GI tumors and associated inflammation. Examples include Carafate® (sucralfate) and Pepto-Bismol® (bismuth subsalicylate).
• For most solid tumors, surgery is indicated. The complete removal of a tumor prior to metastasis can be curative in some cases. Occasionally, restrictions exist on how much tissue can be removed and preserve normal function, as in the esophagus or stomach. In these cases, surgical debulking may be of benefit, where a part of the tumor is removed, giving the patient temporary relief until the tumor grows back.
• Chemotherapy has been used successfully most often in lymphoma cases. There are many protocols available, and the particular regime should be tailored to the patient. Depending on the extent and location of lymphoma, some of these patients do well for months.
• Radiation therapy may be used as a sole entity or in conjunction with surgery. Only certain tumor types are responsive. Very specialized equipment and facilities are needed, therefore these patients are best served in a referral institution.