Mast cell tumors are cancerous growths. The tumors are made up of cells called mast cells. Mast cells are defense cells normally present in your dog’s body. Mast cells’ main job is to defend the body against parasites by releasing a substance called histamine. Mast cell tumors form when these mast cells suddenly begin to proliferate.

Mast cell tumors are mainly found on the skin, but they can occur in other places including under the skin, the liver and the spleen. If the tumor is on the skin and thus visible it will likely be round, raised, and red. It can change size fairly quickly, and it may be itchy to your dog.

It is not known how or why mast cell tumor develop. However, it is suspected that dogs who suffer from allergies may have a greater chance of developing these tumors.

Your vet will perform bloodwork and a buffy coat smear in which a blood sample from your dog is spun in a test tube to make a layer of white blood cells rise to the top of the test tube. The layer of white blood cells is then examined under a microscope. Other diagnostic methods your vet may use include x-rays, ultrasound, lymph node aspirate (using a needle to take a small sample of your dog’s lymph nodes), and fine needle aspirate of internal abdominal organs. These diagnostic methods will allow your vet to classify the tumor or tumors by stage and grade. The stage classification is based upon tumor number and location plus if the tumor(s) have been removed. The grade classification is based on the behavior of the cells analyzed by your vet. Taken together, these two classifications will help your vet decide how to treat the tumor(s).

The tumor(s) will be ranked from stage 0 to stage IV. Stage 0 means that there was one tumor which has been removed by your vet, but some mast cells remain. However, the lymph nodes have not yet been impacted. Stage I means that a single tumor is present on the skin, but no lymph nodes are impacted. Stage II means that there is a single tumor on the skin, and adjacent lymph node are impacted. Stage III means there are multiple tumors present, with or without lymph node spread. Stage IV means single or multiple tumors are present that have spread to distant locations in your dog’s body.

The cell behavior of the tumors are given a grade from I to III. Grade I is given if the analysis suggests the tumor or tumors will not spread to distant locations in your dog’s body. Grade II is given if the analysis suggests that there is about an equal probability that the tumor(s) will or will not spread. Grade III is given if the analysis suggests that there is a high probability that the tumor(s) will spread to distant locations in your dog’s body. Obviously, grade I is the preferred grade.

Treatment is dependent upon the grade and stage of the mast cell tumor(s). Surgical excision, radiation therapy and chemotherapy are various treatments used individually or in combination to treat mast cell tumors. In addition, in June 2009, The Food and Drug Administration (FDA) approved a drug, called PALLADIA™ (toceranib phosphate), to treat canine mast cell tumors with or without regional lymph node involvement. PALLADIA, administered orally to your dog, works by killing tumor cells and stopping blood supply to the tumor. In a clinical study of PALLADIA, approximately 60% of dogs had their tumors cease growing, shrink or disappear. The most common side effects of PALLADIA include diarrhea, vomiting, lethargy, and decreased appetite. Pfizer Animal Health, the company that manufactures PALLADIA, says that it plans to make PALLADIA available for prescription- only purchase in early 2010. However, it will begin rollout of the new drug in the upcoming weeks and months by making it available to boarded specialists.

It is not known how to prevent the formation of these tumors.

No, you cannot  get mast cell tumors from your dog.