Canine Mast Cell Tumor Treatment with Cimetidine for Dogs

Canine mast cell tumors occur in the skin and other bodily tissues. It can develop in pets of all age ranges and all breeds. Mast cells are present in all tissues in the body, and are responsible for the body’s response to infection or inflammation. They are an important defense mechanism and are composed of proteolytic enzymes, histamine and heparin. 

Mast Cell Tumors

Although mast cells are essential for normal body functioning, certain cells produce chemicals in the body that cause ulcers and internal bleeding. A mast cell tumor is a cancerous formation that can spread to other parts of the body and affect the dog’s quality of life. Mast cells that produce excess chemicals cause severe damage to the dog’s body.

Location of Mast Cell Tumors

  • Skin
  • Liver
  • Spleen
  • Bone marrow
  • Intestines

Diagnosis of Mast Cell Tumors

There are various tests that are performed to establish a correct diagnosis. The vet will initially conduct a fine-needle aspirate to obtain a sample for biopsy. The vet will also conduct a surgery to remove the entire tumor for further biopsy. Pets will be subjected to blood tests, urine analysis and x-ray. During the biopsy the tumor will be assigned a grade to determine the severity and prognosis. Grade 1 tumors are more common and most pets with grade 1 tumors respond positively to the treatment.

Treatment of Canine Mast Cell Tumors

The first step during mast cell tumor treatment is surgical removal of the tumor. If the tumor is specific to an area in the body, the vet will also remove extra tissue that surrounds the tumor. Tumors may also be treated with radiation therapy, which effectively controls the growth of cancer cells. The vet will then schedule several follow up visits that include further biopsies to check for disease progression.


Cimetidine is often used to treat and prevent ulcer formations in the pet’s intestine and stomach. Cimetidine works to adjust the pH balance in the stomach by blocking the histamine-2 receptor. Although the drug is registered for use in humans, it may only be administered to pets according to vet instructions. Cimetidine is also known as histamine a2 antagonist, as it reduces acid formation in the stomach. It’s available in tablets of 200, 300, 400 and 800 mg. Some vets prefer to use cimetidine soon after localized surgery, or along with radiation therapy to prevent gastric ulcers. Although it may not be beneficial to pets with high grade cancer, it can help to reduce the effects of mast cells on the gastrointestinal tract.

Conditions Treated with Cimetidine

  • Gastric ulcers
  • Duodenal ulcers
  • Gastroesophageal reflux disease
  • Control of gastrointestinal bleeding

Risks of Cimetidine Administration

Cimetidine is also available in injection form. The medication shouldn’t be administered to pets with liver and kidney disease. A few pets may also be allergic to the drug. Since the drug reacts with certain medications, it cannot be used in combination with metoclopramide, diazepam and sucralfate. Known side effects of cimetidine include constipation, diarrhea and insomnia.

Pets require adequate home care soon after surgery. The surgery along with cost of anesthesia and medical treatment might work out to be very expensive. Pet owners should talk to the vet to determine the best treatment option suited to their dog.