Canine Mast Cell Tumors.

This is follow up from my first case which is found at :
http://drbsvetbuzz.blogspot.com/2012/02/what-is-your-diagnosis-case-1-lumpy-lab.html

This is a case that is dear to my heart as it is my own dog, Tahoe.  Tahoe is a 11 year old lab mix that I have had since I was a senior in veterinary school.  She is often in the clinic with me, or in my Subaru Outback waiting to go for a run.  She is the best dog I have ever had (and I have had a lot), a real one of kind dog.  She has one major flaw though, she gets lots and lots of tumors. Tahoe's growths are typically what is called a mast cell tumor (MCT).

I have a saying that you might hear me use in the exam room, "A lump is just a lump until I stick a needle in it.".  Not sure when and why I started saying this, but it is true all the same.  Your pets growth or lump you've felt while petting is just a growth until a fine-needle aspirate is taken.  A fine needle aspirate, is a simple procedure that typically can take place in the exam room.  A small gauge needle will be inserted into the mass, and a small amount of cells will be retrieved. The cells will then be stained or sent to a special lab and may eventually look something like the cells in the image above.

Mast cells are cell of the immune system and can be found throughout the body and skin.  As seen in the image above they are cell that has tiny granules containing different chemicals that cause inflammation.  Probably the most important mast cell chemical affecting the skin is histamine.  Mast cell tumors are the most common skin tumor in dogs, accounting for roughly 20% of all reported skin tumors.  These tumors are often single firm growths that may be coming form the skin (cutaneous) or under the skin (subcutanous).  They may or may not be haired, ulcerated, reddened or painful.  They may feel like a lipoma (a simple benign fatty tumor) if located below the skin.  Like I stated before, these are like any other lump until I stick a needle in it and they are just a lump.

Both professionally (on patients) and personally (on my own pets) I have seen that MCT can behave a little differently.  They will be a firm mass one day and then almost gone the next day.  Then a few days later they are back and firm.  This is because they are such a reactive type growth and the release of histamine and heparin can make the growth change several times.

Once I stain my aspirate and look at it under the microscope, the diagnosis is made.  Sometimes I will send these a pathologist (a veterinarian that specializes in diagnosis of diseases or pathology), for another opinion or further classification of the diagnosis.  MCT's are very unpredictable in their behavior, meaning that they can be a tumor that has a very slow growth rate or they can be a tumor that is extremely aggressive.  Sending it to a pathologist can often tell me what grade the tumor is, and allow me to form a better treatment plan.

MCT's can have metastatic sites, areas where cancerous cells have spread to but it is not very common.  In the next follow up blog post, I will talk about the treatment for mast cell tumors and also other factors that would influence how a patient would do if they had a MCT.

The take away points are:

• A growth is just a growth until you stick a needle in it!  Any growth that you find should be pointed out to your veterinarian and if possible a fine needle aspirate taken.  All types of tumors are easier to remove when smaller, and a cure can be achieved.  And yes I know some dogs have ALOT of lumps and bumps, and luckily most of these will be benign but, I have removed 7 MCT from my own dog so you never know.
• Mast Cell Tumors (MCT) are the most common skin tumor in the dog.
• Mast Cell Tumors (MCT) are composed of mast cells which are cell of the immune system and they are a granular cell that contains histamine and heparin.