Most times when you notice lumps under your dogs skin they're usually just fatty tumors which are benign meaning that the fatty tumors are not cancerous.
Although it's still a good idea to take your dog to the vet if possible to get tested to be sure those lumps or lump is not cancerous but most times it's just fatty tumors.
They both feel and look the same so it's best to have the dog tested to find out for sure if the lumps are cancerous or not.