What you've found on your dog is what is medically referred to as a "Mast Tumor Cell." These "mast cells", as they commonly called, are a product of your dog's immune system, and are usually associated with an allergic reaction. But the problem with these masts is that they can become malignant or cancerous. Don't panic, not all mast cells are cancerous, but it is important for you to immediately get your dog checked out the minute that you notice or feel one.
Mast cells are known in the veterinarian community as "the great pretenders" because of their ability to change appearance. They can be a hairless and pink. They can be a raised lump, just under your dog's skin or fur. They can form on the outside or inside of your dog's mouth! As I said before, not all mast cells are cancerous. To be sure about the makeup or diagnosis of any lump that you find on your dog's body, you should immediately take your pet to your local vet.
While at the vet, your dog's mast will be checked out to determine exactly what it is. The only way to find out if its cancerous or non-cancerous is for your vet to take what is called a "needle aspiration biopsy." What happens in this procedure is a needle is inserted into the mast cell and a small amount of material is extracted from the lump. This material is then examined under a microscope to determine whether or not it is cancerous or benign. This is your dog's ONLY defense against a major surgical procedure. It is considered to be a safe and minor surgical procedure.
From this procedure, your vet can then determine the diagnosis and what treatment options that you have available for your "best friend." I cannot emphasize this enough! If you find a lump on your dog:
1. Go get him/her checked out the local vet immediately!
2. Don't panic! All lumps found are not always cancerous!
In the end, your local veterinarian will be able to give you the peace of mind and prescribe the right treatment if it is determined that your dog has cancer. Like all cancer, if caught early, there is a good chance of recovery. You just have to be vigilant and pay attention to your "best friend." Good luck!