Most lumps and tumors or other growths on dogs are not cancerous.
If the lump or bump is soft, squishy and moveable then it's most likely just a cyst that is usually not harmful to your dog but if the lump is hard or getting larger then it could be a cancerous tumor but could also be a non cancerous tumor.
There's no way to tell for sure if the lump your dog has is cancer by just feeling it but it can be an indicator and if you think the dog may have a tumor that is cancerous you should have the dog examined as the vet can do Xrays and other procedures on the dog to check whether the tumor is cancerous.
However it's normal for dogs to develop bumps and lumps inside their body as they age.