Multiple Mast Cell Tumors in Dogs

Lili Duda, VMD
Last Modified: November 1, 2001

Dear OncoLink "Ask the Experts,"
I have a 5-year-old female Pitbull mix. I took her to the vet about 5 months ago to look at her "warts." She had one on her eye, and forearm. He told me they were just warts, and not to worry. Well, it turns out, they were mast cell tumors. Anyway, she had 13 different little warty things removed, 12 were mast cells (the eye was papilloma).

They were all grade I. He said the margins were clear. But why does she have them all over her body? He said I should have an aspirate taken from her spleen, liver, and bone marrow. He said he has never seen multiple sites of grade I tumors before.  
Please help me to sort this out.

Lili Duda, VMD, Editor of the OncoLink Veterinary Oncology Section, responds:

You might consider having the dog "staged" for mast cell tumor. This staging would include: CBC, blood chemistries, abdominal ultrasound (and needle aspirates if the liver or spleen look abnormal), buffy coat smear, bone marrow aspirate, and needle aspirates of any lymph nodes if enlarged.

In general, the treatment of grade I mast cell tumors is surgical removal—if surgery obtains "clean" margins then this is usually adequate. Grade I mast cell tumors generally have a relatively benign behavior.

However, mast cell tumors can behave unpredictably. The fact that there are multiple tumors indicates that some form of systemic treatment might be warranted (such as prednisone or other chemotherapy)—however this depends to a large extent on the results of the staging evaluation.

We have seen a group of dogs that develop multiple mast cell tumors either with multiple tumors at the same time or multiple tumors over the years. Some dogs and some breeds of dogs seem predisposed to developing multiple tumors. However, if there is no evidence of spread to lymph nodes or other organs, many of these dogs can be successfully treated by surgical removal of the tumors particularly if the tumors are small (with or without some form of chemotherapy) and close monitoring for new tumors.

If you or your veterinarian have not already done so, please consult a qualified veterinary oncologist to further explore the treatment options for your pet.