Simba is a rescue dog that has recently been adopted. His new owner discovered a red small lump under his neck. I collected a fine needle aspirate of the lump and examined it under the microscope. I informed the owner it was most likely a histiocytoma. I gave her the option of confirming the diagnosis by a pathologist and she opted for that. This lump is an allergic type of lump that commonly occurs in young dogs. It can go away on its own. It is crucial to always check it out as it looks identical to a mast cell which is a very nasty type of skin lump in dogs.