You're sitting on the couch at the end of a long day patting your dog. As you stroke along his belly you feel something different and new. There is a lump there. It's small and it doesn't seem to be bothering him. He seems quite happy and well in himself. But this lump... should you be worried?
Well, yes. Until tested that lump could be anything from nothing very much through to something quite scary. Until proven to not be a problem it's very reasonable to be concerned. A lump could be as innocent as a skin tag or wart or benign growth. Or it could be a tumor that requires surgical removal and possibly follow up treatment.
The best thing you can do for your pet is get that lump identified.