Practically speaking, all dog owners need to know about mast cell tumors (MCT), as they can affect any dog and can look like anything. They are often found as a lump in the skin, but can also be a lump under the skin (subcutaneous tissue). The easiest way to diagnose them is to take a fine needle aspirate (FNA) of the lump and look at the cells under the microscope. I always send my samples to a reference lab, as in-house samples may miss mast cells if you are using Diff-Quick staining.
Once we diagnose a MCT, the lump needs to be removed with large margins. That means that even a pea-sized lump will need to have at least 3cm of skin taken in all directions, and you remove 1 tissue layer deep (e.g. removing all the skin, but also the layer of fat underneath). Sometimes the tumor is in a bad location, like the limbs or the face, and, in order to get complete removal, an amputation is done.
MCTs should be taken seriously, as they can spread through the skin and also to other organs (metastasize). We can't tell which tumors will do this based on the FNA alone, so once the tumor is removed, we submit it for further testing. We can also run bloodwork and do an abdominal ultrasound to check for signs of metastasis.
The best thing to do is to check your dog regularly, and bring any lumps to your veterinarian's attention, particularly if you have an at risk breed, including Boxers and any Pit Bull or related bully breed.
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