Overview of Canine Mast Cell Tumors (Mastocytoma)
Mast cell tumors, also called mastocytomas and commonly abbreviated as MCT, arise most commonly in the skin. They develop from a normal component of body tissues called the mast cell that play a role in the process of tissue repair by releasing inflammatory mediators.
Malignant mast cell tumors can spread to the lymph nodes, spleen, liver and bone marrow. Mast cell tumors are among the most common tumors of dogs, accounting for approximately 20 percent of all skin tumors. The cause of mast cell tumors is unknown.
Dogs that develop mast cell tumors often are older (usually 8 to 9 years of age), although they can occur in dogs of all ages.
What to Watch For
Signs of Mast Cell Tumors in dogs may include:
Diagnosis of Mast Cell Tumors (Mastocytoma) in Dogs
Diagnostic tests are needed to recognize mast cell tumors and exclude other diseases that may cause similar symptoms. Tests may include:
Treatment of Mast Cell Tumors (Mastocytoma) in Dogs
Treatment for mast cell tumors may include one or more of the following:
Home Care and Prevention
Your dog should be examined by a veterinarian if you notice any mass on his skin. A fine needle aspirate or surgical biopsy can be performed to identify the nature of the mass. Most skin tumors in dogs are benign, but early detection and treatment of malignant tumors, especially mast cell tumors, can dramatically affect your pet’s long-term prognosis.
No method of protection against development of mast cell tumors can be recommended because the cause of these tumors is unknown. Careful monitoring of your pet is important, especially if you have one of the breeds known to be at increased risk. If you notice a lump in your dog’s skin, the mass should be examined by a veterinarian as soon as possible.
In-depth Information on Canine Mast Cell Tumors
Mast cell tumors or mastocytomas arise most commonly in the skin. They develop from a normal component of body tissues called the mast cell, which normally plays a role in the process of tissue repair by releasing inflammatory mediators.
Mast cell tumors vary greatly in their biological behavior. Some mast cell tumors remain localized for extended periods of time, but others invade local areas causing much inflammation, and they eventually metastasize or spread to distant sites in the body. Malignant mast cell tumors can spread to the lymph nodes, spleen, liver and bone marrow. Mast cell tumors are among the most common tumors of dogs, accounting for approximately 20 percent of all skin tumors.
Mast cell tumors occur as one of three types:
This classification refers to how closely the mast cells of the tumor resemble normal mast cells and ultimately to the biological behavior of the tumor or its tendency to remain localized or spread throughout the body.
Well-differentiated Mast Cell Tumors
Poorly-differentiated Mast Cell Tumors
Moderately-differentiated Mast Cell Tumors
This type is between well and poorly differentiated.
The cause of mast cell tumors is unknown. Mast cell tumors have been transmitted experimentally using tumor extracts suggesting possible viral origin, but this hypothesis remains unproven. Dogs that develop mast cell tumors often are older (usually 8 to 9 years of age), but mast cell tumors can occur in dogs of all ages. Breeds that seem predisposed include boxers, Boston terriers, bull terriers, bullmastiffs, English setters and golden retrievers. Males and females are affected equally.
Mast cell tumors generally respond well to treatment. Well-differentiated mast cell tumors in the skin often can be removed successfully by wide surgical excision. The less common, poorly-differentiated mast cell tumors can cause severe swelling and inflammation locally and tend to spread throughout the body. These aggressive tumors are much more difficult to treat effectively and often result in death. Mast cell tumors that occur in areas around the mouth, anus and genitals tend to be more aggressive and have a worse overall prognosis than those occurring elsewhere in the skin.
Appearance can vary but mast cell tumors are usually round, raised masses in the skin. They can be covered with hair or hairless, and the affected skin may be reddened and ulcerated and may bleed. Mast cell tumors have the unique characteristic of growing and shrinking in size rapidly over short periods of time due to the release of inflammatory chemicals from the mast cells of the tumor with minor trauma. In animals with mast cell tumors of the spleen or intestinal tract, clinical symptoms of inappetence, vomiting, abdominal pain, and black tarry stools can be seen.
Many tumors, both benign and malignant, can affect the skin of dogs. The most common are:
In-depth Information on Diagnosis
Diagnostic tests are needed to recognize mast cell tumors and exclude other diseases that may cause similar symptoms.
Mast cell tumors are graded as follows:
Grade I (well-differentiated)
Grade II (moderately-differentiated)
Grade III (poorly-differentiated)
In-depth Information on Treatment
Depending on their grade of differentiation, mast cell tumors often can be effectively treated. Treatment for mast cell tumors may include one or more of the following:
In dogs with especially large tumors or tumors located in regions of the body that are difficult to manage surgically, referral to a specialist in veterinary surgery may be advisable.
The surgeon also should remove any enlarged lymph nodes in the area of the tumor because the tumor may have spread to these local lymph nodes. If any of the removed lymph nodes contains tumor cells, follow-up chemotherapy will be needed.
Dogs with incompletely excised tumors should be referred to a veterinary oncologist for consultation on additional treatment options. Some Grade II and all Grade III tumors behave in a malignant fashion and may require chemotherapy to manage the disease.
For dogs with Grade I mast cell tumors, complete surgical excision carries an excellent prognosis with more than 90 percent of affected dogs alive without disease after 4 years.
For dogs with Grade II mast cell tumors, there is a wide spectrum of biological behavior, but approximately 50 percent of affected dogs survive for 4 years without tumor recurrence.
For dogs with Grade III mast cell tumors, the prognosis is poor with surgical excision alone, and less than 10 percent of affected animals survive for 4 years. It often is impossible to completely excise Grade III tumors.
Radiation therapy also may be recommended after surgery if the removal of the tumor was thought to have been incomplete based on the pathology report that tumor cells were observed in specimen margins. Radiation therapy can be a very effective treatment for incompletely excised Grade I and II tumors with control rates approaching 90 to 95 percent at five years. Radiation therapy may also be used in conjunction with surgery and chemotherapy to treat animals with Grade III mast cell tumors. In this situation, the life span of affected animals may be prolonged and their quality of life improved.
Drugs used in chemotherapy have potentially serious toxic effects and should only be administered by veterinarians experienced in their use.
The success of chemotherapy in treating pets with malignant mast cell tumors has been mixed and overall chemotherapy should be viewed as palliative, which means it will improve your pet’s quality of life and prolonging survival.
Mast cell tumors contain several chemical mediators of inflammation that can cause adverse reactions in your pet either in association with the tumor itself or when the tumor cells die during chemotherapy and release these inflammatory mediators. Potential adverse effects include stomach ulceration, generalized itchiness and, in unusual instances, massive release of inflammatory mediators with a potentially fatal allergic reaction called anaphylaxis. Additional drugs to counter the effects of the inflammatory mediators released by mast cell tumors may be prescribed for your pet. These drugs include anti-histamines such as diphenhydramine, H2-blocking drugs such as cimetidine, ranitidine or famotidine and ulcer-coating agents such as sucralfate.
Follow-up Care for Dogs with Mast Cell Tumors
Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up can be crucial. Administer as directed any prescribed medications and call your veterinarian if you have difficulty administering them.
Restrict your dog’s activity during the time he is recovering from surgery, usually 10 to 14 days, to allow for proper healing of the surgery site.
Your pet may be placed on a 7- to 14-day course of antibiotics to prevent infection from developing at the site of tumor removal.
Your veterinarian may prescribe a short course of anti-inflammatory analgesic medications. In cases in which radical surgery was necessary, your veterinarian may prescribe narcotic analgesic medications. These medications may be given by mouth or in the form of a patch applied to the shaved skin. The patch is placed on your pet’s shaved skin and the narcotic is absorbed slowly over several days, delivering constant pain relief.
Your dog usually will need to have sutures removed from the skin 14 to 21 days after surgery after healing has occurred.
The veterinary pathologist’s biopsy report will help your veterinarian (often in consultation with a veterinary oncologist) decide if your dog needs additional treatment such as chemotherapy or radiation therapy.
Even if no follow-up treatment is recommended, your pet should be evaluated on a regular basis for recurrence or spread of the mast cell tumor. Follow-up examinations are recommended every 2 to 3 months for the first year and then every 6 months thereafter for dogs with mast cell tumor. Your veterinarian will take a complete history and perform a thorough physical examination during re-evaluations, and may also perform buffy coat smears to check for circulating mast cells.
You should examine your pet routinely for signs of recurrence at the site of tumor removal or for new masses. Unfortunately, dogs that develop one mast cell tumor may have a tendency to develop others during their lifetime. If you detect any skin masses, contact your veterinarian for a re-evaluation visit.
Signs to watch for that may indicate spread of the mast cell tumor may include decreased activity, decreased appetite, vomiting or diarrhea. If you note any of these signs, contact your veterinarian to schedule a re-evaluation visit.
If your dog receives either radiation therapy or chemotherapy, your veterinary oncologist will instruct you on proper follow-up.