This kind of lump/growth needs to be ideally assessed by your veterinarian to have a definitive and specific answer and take any decision. Usually there are two ways your vet can do that a part from examining it directly during physical examination. A biopsy can be taken under local or general anesthetic, otherwise a smaller sample through a fine needle can be aspirated (this technique is called FNA= fine needle aspiration). Differentials include skin cysts, infections, benign or more sinister type of tumors. Hope this answer was helpful, but please do not hesitate to contact us again on the forum or by requesting a consultation if you have any more questions or to discuss it any further.