I was just grooming my Westie who is 6 years old, and I don't remember a lump being there when I last groomed her. It is right between her front legs, a little bit above where her leg joints are - maybe like 1-2 inches above. I am so worried!!! I'm hoping that it's something that I just didn't notice before, but I don't remember feeling it before.
If it is soft and squishy, it is probably a fatty tumor. Alot of dogs get these, and don't worry about it unless it gets large, or interfers with movement.
If it is hard, like a rock, then that could be cancer. It is a good idea to have your vet check it IN EITHER CASE, just to be on the safe side. I have seen soft tumors become cancer.
The other thing, is take a index card and trace around the lump. This will give you a size. As it continues to grow(if it does), you will exactly how much. Always keep that card with your other doggie info, that way you always have it to refer back to.
Chances are it is nothing, but ALWAYS have lumps checked by a vet to be on the safe side.