I cannot tell you how many times a day I get asked this same questions, Doc is this a cancerous mass? Does my animal have cancer? Unfortunately, if we have yet to do any testing on their pet my answer is always “maybe or maybe not.” This article is going to focus on skin and subcutaneous masses (masses just under the skin), not masses that are palpated in the abdomen or caught on screening x-rays. Contrary to what some veterinarians will tell you, you cannot determine the type of mass by just feeling and looking at it. Yes masses can have all the characteristics of being benign - slow growing, not painful, not red or inflamed, smooth, and then still end up being cancerous. Also, despite what you may read on the internet, routine blood work will almost never tell you that your pet has cancer. The exception to that is Lymphoma, where the white blood cell lines may be extremely elevated.
So what do you do if your dog has a mass?
Be prepared for diagnostics. This means that a fine needle aspirate will be obtained. A fine needle aspirate is when the veterinarian will take a needle and poke it into the mass to try to obtain some of the cells of the mass. Those cells are then evaluated under a microscope. 75% of the time we are able to make a diagnosis of the type of mass by the fine needle aspirate (FNA). Some masses are very exfoliative, which means they will shed the cells into the needle nicely, but some are not. If the FNA does not give definitive answers the next step would be to obtain a punch or wedge biopsy of the mass. This means, under anesthesia or heavy sedation, a bigger piece of the mass will be obtained to get a better idea of the mass. Some masses that are very small may just be surgically removed if the FNA is not diagnostic, but in those cases large surgically margins must be obtained just in case the mass does come back cancerous.
But Doc, can’t you just remove the mass?
Yes we can, however if we know what type of mass we are dealing with we are better able to judge how invasive we need to get with our surgery. If a mass is benign, I will just remove the mass and not worry about getting a lot of extra tissues around it. If I know a mass is cancerous, then there are guidelines about how much extra tissue needs to be removed to ensure that there are no cancerous cells left behind. If cancerous cells are left behind, it may allow for regrowth of the mass or require additional treatments like radiation therapy the area.
Do I need to biopsy the mass?
Yes. You were concerned enough about the mass to remove it, why would you not want to know what it is. If it is cancerous, we may want to do additional monitoring or treatments to make sure that it does not regrow. We also will find out if there is a chance that any cancerous cells were left behind. If it is benign then you get to rest easy and not worry about the mass anymore.
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