Gastrointestinal Neoplasia in Dogs
Dr. Bari Spielman
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. Intrathoracic masses/growths may put pressure on the esophagus from the outside, creating a blockage
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 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:
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
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.