Gastrointestinal (GI) neoplasia (cancer) occurs infrequently in cats as compared to neoplasia involving other systems. Over two-thirds of GI neoplasms in cats 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 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. Intrathoracic masses/growths may put pressure on the esophagus from the outside, creating a blockage
Megaesophagus, which is a distended and/or poorly functional esophagus, is a more common condition in cats, 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
Lymphosarcoma is the most common gastric and small intestinal tumor of cats. In general, the most common tumors seen in the stomach and small intestines of cats are adenocarcinoma, lymphosarcoma, leiomyosarcoma, leiomyomas, fibrosarcoma, squamous cell carcinoma, plasmacytoma and mast cell tumors. The ingestion of certain drugs may cause gastrointestinal ulceration, vomiting (with or without blood) and inappetence.
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.
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. 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.
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
Lymphosarcinoma is the most common tumor of the colon in cats. 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. Infectious agents (bacterial, viral, or parasitic) often cause blood and/or mucus in the feces.
Colonic/rectal disorders include:
Constipation causes straining to defecate and needs to be differentiated from colonic/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.