Gastrointestinal (GI) Neoplasia in Dogs
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.