What is this red lump on my dog's leg?

Dr. Marie replied:

Thank you for the excellent photos that you sent me of this red lump on your dog's leg. I have included one photo here:



It is always hard to talk about lumps without being able to feel and see the lump in person. While I can't give you a diagnosis online, I can tell you that I am a little concerned by what I am seeing.

There are a few possibilities for what this could be, but the two most common lumps that can look like this are either a mast cell tumor or a histiocytoma.

A mast cell tumor in this location (on the leg) has the potential to be serious. There are different grades of mast cell tumors and many of them can be cured with surgery. However, some can be serious types of cancers. Mast cell tumors can be itchy because they can release histamine.

A histiocytoma can look exactly like this as well. Fortunately a histiocytoma is not usually a serious issue. These lumps appear for no reason and then eventually after a month or two go away on their own with no treatment. Histiocytomas are more common on younger animals, but I have seen them in animals of all ages.

It could be something else like a reaction to an insect sting or a strange cyst or something else but I think that either a mast cell tumor or a histiocytoma are most likely.

I would highly recommend a vet visit as soon as possible for this. I don't mean to be alarmist, but if it is a mast cell tumor then the sooner it is dealt with the better. If it is a histiocytoma, well then at least you know you don't need to worry. The vet will do a test called a fine needle aspirate where they put a tiny needle in the mass and draw some cells out. Most dogs tolerate this really well. The vet will look at the cells under a microscope or may decide to send it to a lab to look at. It is usually quite easy to tell the difference between mast cell tumors and histiocytomas.

I hope everything goes well. I would really appreciate if you are able to post back to this question once you get a diagnosis.

Thanks,
Dr. Marie.


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Dr. Marie replied:

I am not familiar with this ointment but I can guarantee you that there is no ointment or cream that will take this away!