I looked also. Odd looking and I agree with Blu. Not sure why the Vet tested for worms. You may want a second opinion.
I looked at the picture. And I am surprised that your vet did not give you a diagnosis. I am also surprised that he did not do a fine-needle aspiration (where they use a needle to suck cells from the lump to look at under a microscope). If nothing was found after that, a biopsy should have been performed, where they remove part of the lump and send it off for testing. Only after all that, and a diagnosis of cancer or someother malignacy is found, should surgery be considered. Your dog is young, and should handle these procedures well. Your pocket might not like it, tho. Blessings - Blu