Tumors of the Small Intestine

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Article Written by Dr. Daniel A. Degner, Board-certified Veterinary Surgeon (DACVS)

Animal Surgical Center of Michigan

5045 Miller Road

Flint, MI 48507


Phone: 810-671-0088

Key Points

Most common intestinal tumors are lymphoma, leiomyosarcoma and adenocarcinoma

Leiomyosarcoma is commonly associated with bowel rupture and peritonitis

Overall prognosis is favorable for gastrointestinal stromal cell tumors (previously grouped in the leiomyosarcoma class)


The digestive tract, located within the abdomen, consists of the stomach and intestines. Dogs and cats have a very long small intestine which digests food and absorbs nutrients into the body. The colon is a reservoir that holds feces. The lining of the intestine, called the mucosa consists of glandular cells that secrete mucus and epithelial cells that absorb nutrients. Beneath the lining layer is the lamina propria which contains many lymphocytes, and lesser numbers of mast cells and plasma cells. The final two layers include a connective tissue layer and then a layer of smooth muscle that propels food down the intestinal tract. The importance of the anatomical description is that various tumor types can form from each of these layers. For example, adenocarcinoma comes from the epithelial cells, lymphoma, mast cell tumor and plasmacytoma come from the lamina propria, fibrosarcoma and gastrointestinal stromal cell tumor originate from the connective tissue layer and leiomyosarcoma originates from the muscle layer.


Intestinal tumors

The most common types of intestinal tumors include lymphoma, adenocarcinoma, and leiomyosarcoma. Approximately 70% adenocarcinoma tumors metastasize, and 30 to 50% of leiomyosarcoma tumors metastasize. These two tumor types most commonly afflict Collies and German Shepherds. The Siamese develop intestinal adenocarcinoma more often than other breeds. Lymphoma has two forms that are most commonly seen in the intestine. One form diffusely infiltrates the intestine and the other form is a gross mass within the intestinal wall. The diffuse form frequently infiltrates the entire bowel, therefore nutrients are not absorbed well from the intestinal tract. In cats. a specialized DNA test (called PCR) has implicated the feline leukemia virus to be an underlying cause in some cases. Less common tumors include mast cell tumors, plasmacytomas, fibrosarcoma, extraskeletal osteosarcoma, and gastrointestinal stromal cell tumors.


l Signs and diagnosis

Vomiting, diarrhea, anorexia, depression, weight loss, and dehydration are common nonspecific signs of an intestinal tumor. An intestinal tumor can weaken the bowel, thus causing it to rupture. With leakage of contents into the abdomen, a serious infection results. Clinical signs of this may include acute depression, vomiting, fever , abdominal pain, crying, not willing to lie down or sitting in a praying position.

Abdominal ultrasound is a very useful tool used to diagnose an intestinal mass. Complete blood count, chemistry, and urinalysis results are used to check the health of the intern organs. Chest x-rays are used to identify visible (macroscopic) evidence of spread of cancer to the lungs and lymph nodes.


The day of surgery

The anesthesia and surgical team will prescribe a pain management program, both during and after surgery that will keep your companion comfortable. This may include a combination of general anesthesia, injectable analgesics, and oral analgesics.




and the bowel is sutured or stapled together. Biopsies are collected from the intestines, liver, lymph nodes, or another other organs and submitted to a pathologist for evaluation. While in our hospital, the pet will continue to receive intravenous fluids, and antibiotics. The pet is monitored in the intensive care unit for a 2 to 3 night hospital stay.




Once your pet is at home, a prescribed analgesic is administered for a few days to minimize discomfort. A bland diet such as Hill's i/d or Eukanuba Low Residue diet is fed. Alternatively, a home made diet (50:50 mix of cooked chicken breast, turkey breast or lean hamburger and potatoes or pasta) can be fed for 3 days at home followed a period of 3 days during which the diet is gradually transitioned to a normal diet. Exercise is limited to 10 minute leash walks three times daily for three weeks after surgery. The incision should be evaluated daily for signs of infection. A follow-up evaluation is completed by the surgeon or your pet's primary care veterinarian in two weeks after surgery.

Uncommon complications after surgery may include continued vomiting due to inflammation of the intestines and a localized infection of the incision. Peritonitis, an infection of the abdominal cavity, is usually caused by bowel incision leakage that usually occurs within the first 5 days after surgery. Signs of peritonitis may include anorexia, vomiting, fever, and abdominal pain. If the bowel is leaking at the site of the bowel resection, another operation will be needed to repair the bowel.



Overall mean survival time of 21.3 months following leiomyosarcoma was found in one study; in another study the survival time was 8 months. Approximately half of the dogs had bowel perforation, peritonitis, and increased risk of death in the perioperative period. Other reports indicate that the previous diagnosis of leiomyosarcoma in some cases is in error and the actual diagnosis is gastrointestinal stromal cell tumor (GIST). A study that differentiated between leiomyosarcomas and GIST with special testing demonstrated a survival of dogs with leiomyomas to be 8 months versus 37 months in the group that had GISTs.

Following excision of intestinal adenocarcinomas in dogs, the overall median survival has been reported to be 10 months. Dogs with metastasis had a median survival time of 3 months, versus dogs with no visible metastasis had a median survival time of 15 months. The value of chemotherapy is not known at this time, but may be considered in some cases.

Cats that have adenocarcinomas of the intestine with visible spread of the tumor have a median survival time of 5 months after surgery; however, with no visible spread of the tumor, survival time doubles to 10 months after surgery.

Dogs with diffuse intestinal lymphoma generally have very short survival times, however, if a solitary lymphoma tumor in the intestine can be removed and the remaining parts of the bowel do not have extensive diffuse disease; survival is increased to 6 to 9 months with surgery and chemotherapy. In cats, the median survival time is highly dependant on whether the lymphoma is a small cell or large cell (blastic) lymphoma. Patients affected by the small cell lymphoma potentially can survive for 1 to 2 years, whereas the blastic form results in death usually within 4 to 6 months in most cases. One study showed that about 50% of the cats treated for intestinal lymphoma had complete remission with survival times greater than 650 days; 37% had partial remission and a resulting survival time of 122 days.

Mast cell tumor of the small intestine generally carries a poor prognosis with most patients deceased at 2 months postop.



  1. Cohen M, et al. Gastrointestinal leiomyosarcoma in 14 dogs. J Vet Intern Med 2003;17:107110.
  2. Crawshaw J, et al. Prognosis for dogs with nonlymphomatous, small intestinal tumors treated by surgical excision. J An Anim Hosp Assoc 1998;34:451-456.
  3. Milner RJ et al. Response rates and survival times for cats with lymphoma treated with the University of Wisconsin-Madison chemotherapy protocol: 38 cases (19962003). J Am Vet Med Assoc 2005;227:11181122.
  4. Phillips BS. Gastrointestinal tumors. IN: Small Animal Clinical Oncology, 3rd edition. Eds Withrow and MacEwen. WB Saunders, Philadelphia 2001; pp335-346.

Frequently Asked Questions After Surgery

When should my dog have the first bowel movement after surgery?

  • Many dogs will not have a bowel movement for the first 4 to 5 days after surgery
  • Reasons that a dog will not have regular bowel movements after surgery include:
    • The dog has been fasted prior to surgery
    • Dogs do not eat well during the hospital stay
    • They frequently do not eat well when they go home
    • They are fed highly digestible food that produces little stool
    • Pain medication that contain narcotics (such as morphine, fentanyl patches, and tramadol) can be constipating
  • If a pet does not have a bowel movement on the 5th day of being home, a stool softener such as metamucil can be fed
    • Dose of metamucil is 1 tsp per 25 Kg mixed in with each meal (canned dog food); feed immediately after mixing, as the metamucil will gel the food and may make it less palatable

My pet had surgery and will not eat.  What can be done?

  • Dogs
    • Most pets will not eat their regular dog food after surgery, especially if it is kibble.
    • Offer a cooked diet having a 1:1 ratio of a protein source and carbohydrate source.  The protein source can be any meat (example: chicken breast, turkey breast, lean hamburger) that is low in fat and should be cooked (drain off all fat after the meat has been cooked).   The carbohydrate can be pasta, potato or white rice.
    • Try canned dog food; to enhance the flavor sprinkle a very small amount of garlic powder or chicken or beef broth (Chicken-in-a- MugTM or Beef-in-a-MugTM products)
    • Try Gerber strained meats for babies such as the chicken, beef, turkey, or veal
    • Try Hill's A/D diet available at most veterinary hospitals
    • Hand feeding: place a small amount of food in the mouth so that your dog gets the flavor
    • Warm the food slightly in a microwave, as the food will be more aromatic; stir the food before feeding and test the temperature on the bottom side of your wrist; it should only be luke warm.
    • Remember that most pets will not eat the first day or two after they get home from surgery
  • Cats
    • Offer smelly foods that contain fish such as tuna or smelly cat foods
    • Try Gerber strained meats for babies such as the chicken, beef, turkey or veal
    • Hand feeding:  with your finger place a small amount of food on the roof of your cat's mouth; use a syringe to get soft food into the mouth
    • Warm the food slightly in a microwave as the food will be more aromatic; remember to stir the food before feeding and test the temperature; it should be only luke-warm
    • Some cats will only eat dry food, try kibble if your cat normally has been fed that food
    • Petting and stroking your cat frequently will help to stimulate appetite
    • Remember that most pets will not eat the first day or two after they get home from surgery
    • Appetite stimulants such as cyproheptadine may be helpful
    • If your cat refuses to eat anything for 7 days a stomach tube or nasogastric tube should be placed to provide nutrition so that a serious liver problem (hepatic lipidosis) does not develop

My pet is vomiting.  What can be done?

  • The first thing for you to discern is whether your pet is vomiting or regurgitating.  Both will result in fluid or food being brought up.  Vomiting always will have heaving or retching of the abdomen prior to expulsion of the vomitus.  Regurgitation is not associated with heaving and the pet usually just opens the mouth and fluid or food will be expelled.  Usually the regurgited material will be clear or brown colored fluid. 
  • Next is to identify the cause of the vomiting or regurgitation.
  • Causes and treatment of vomiting after surgery
    • When some pets return home after a stay in the hospital they may drink excessive amounts of water at one time and then vomit; if this appears to be the case, the water should be limited to frequent smaller amounts.
    • Medications such as antibiotics, narcotics or nonsteroidal anti-inflammatory medication commonly cause vomiting after surgery.  In order to see which medication is causing the problem, the administration of each drug should be separated 2 hours apart.  Usually the pet will vomit or appear nauseated (drooling and sick look) within 1 hour of administration of the medication that they are sensitive to.  The antibiotic in some cases may be changed to a different one, or may be discontinued. 
    • Stomach upset from anesthesia is a potential cause of vomiting and will pass within a couple of days. 
    • An uncommon cause of vomiting after surgery is internal organ failure.  Blood testing will confirm this problem. For this reason vomiting should not be ignored if it persists for more than 24 hours.
    • If your pet had surgery of the bowels or stomach, vomiting is always a concern, as it may indicate that infection of the abdominal cavity, called peritonitis, is present.  Do not ignore this sign.
    • Symptomatic treatment of vomiting involves withholding food for 12 to 24 hours, then introducing small amounts of bland food such as rice and lean cooked hamburger, if your pet does not vomit after that then gradually wean him/her back onto the regular diet after 3 days.  In order to decrease the acidity of the stomach, Pepcid AC 0.5 mg/kg can be given by mouth twice daily for 5 days.  Metoclopramide and Cerenia are good anti-vomiting medications for dogs and cats.  You should always consult a veterinary healthcare professional before administering medication.
  • Causes and treatment of regurgitation after surgery
    • The most common cause of regurgitation is reflux of acid from the stomach into the esophagus while your pet is under anesthesia.  Acidic fluid from the stomach can cause a chemical burn of the esophagus and result in a bad case of heart burn, called esophagitis.  This results in poor motility of the esophagus, therefore water and food will accumulate in this structure.  In most cases, esphagitis is self-eliminating and will resolve within two or three days. 
    • If the esophagitis is severe the esophagus may develop one or more strictures.  A stricture is a narrowing or stenosis of the esophagus and does not allow passage of food down the esophagus, in regurgitation that lasts longer than one week.  This problem should be brought to the attention of your pet's doctor within the first two weeks so that it can be treated by ballooning the stricture (minimally invasive procedure, as it is done with the aide of an endoscope).  If an esophageal stricture is chronic surgery is needed.
    • Symptomatic treatment of regurgitation caused by esophagitis includes feeding bland food, and administering a coating agent (sucralfate) and an acid blocker (omeprazole or other).  Consult a veterinary health care professional if the regurgitation continues for more than a couple of days.

How do I know that my dog is in pain following surgery?

  • Signs of pain include
    • crying
    • biting if you get near the surgical site
    • grimacing (lips are pulled back and the the dog looks anxious)
    • tragic facial expression
    • panting
    • restlessness and unable to sleep; pacing
    • if abdominal surgery was done the pet will not lie down on the incision, or will continually sit up in spite of appearing very tired
    • the worst pain will be for the first 2 to 3 days after surgery

What can I do to control my dog's pain?

  • Narcotic medications that control pain: tramadol, butorphanol, Duragesic (fentanyl patch)
  • Anti-inflammatories used to control pain: Deramaxx, Rimadyl, Previcox, or Etogesic
  • If an orthopedic surgery has been done cold packing the surgical site may be helpful
    • A cold pack may be a pack of frozen peas, crushed ice in a Ziploc bag, or a cold gel pack; place a thin barrier between the skin and the cold pack.  An alternative to a cold pack is to freeze water in a styrofoam cup; after frozen cut the bottom of the styrofoam cup out. Cool the surgical site around the incision by rubbing the exposed ice directly on the skin in a circular pattern.  Cooling the surgical site helps to numb the area.

How do I know that my cat is in pain following surgery?

  • Pain is more difficult to assess in cats versus dogs, as signs can be more subtle and they usually do not vocalize when in pain
  • Signs of pain in a cat include the following:
    • biting if you get near the surgical site
    • growling or deep cry
    • not wanting to eat
    • hiding and not wanting to be near owner (remember that this could also be caused by the cat just being upset about leaving home and coming back)

What can be done for pain at home for my cat?

  • Pain medication such as buprenorphine or a Duragesic (fentanyl) patch
  • Tylenol will kill a cat as they lack abundant glutathione enzyme in the liver
  • Anti-inflammatories can be used, but the dose is much less than dogs

Is it okay for my pet to lick the incision?

  • If a dog licks the incision, the healing process may be delayed.
  • Licking can remove stitches and cause the incision to open
  • Licking can become a severe habit that is difficult to break
  • Licking can cause infection as the mouth has many bacteria
  • Dogs will frequently lick the incision when the owner is not watching such as at night time; if the skin looks red or excoriated the most common cause is from licking.
  • To stop your pet from licking the following can be tried:
    • Elizabethan collar can be placed on the neck; this will not help stop your pet from scratching at the region
    • Cervical collar (bite not collar) is a less awkward device and can be effective at stopping a pet from licking the surgical site
    • A tee shirt can be used to cover an incision on the chest or front part of the abdomen; gather the waist of the shirt up over the dog's back and wrap an elastic band around this part of the shirt.
    • A bandage or sock can be used to cover an incision on a limb; fasten the top of the sock to the dog's limb with tape.
    • Bitter apple can be applied around the incision; many dogs will continue to lick  after application of this topical
    • Bitter Apple and Liquid HeetTM (obtain this from a drugstore...it is used for sore muscles) mixed in a 2:1 ratio can be applied around the skin incision
    • Antipsychotic medication in some cases is needed

Board-certification by the American College of Veterinary Surgeons

What does it mean?

  • Four years of advanced training in surgery beyond the Doctor of Veterinary Medicine Degree

  • Experience in the development of new surgical treatments

  • Rigorous examination by the American College of Veterinary Surgeons to ensure competency in advanced surgical techniques

  • Assurance that a veterinarian is a surgical specialist

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