An eyelid tumor can take on many different appearances in dogs, depending on the type of tumor and its location. The most common types of eyelid tumors are adenomas, which are benign growths that originate from the glands in the eyelid. Adenomas typically appear as small, round, white or flesh-colored bumps on the surface of the eyelid. Other types of tumors that can affect the eyelids include basal cell carcinomas, squamous cell carcinomas, and melanomas. Basal cell carcinomas are slow-growing tumors that originate from the cells lining the base of the hair follicles, while squamous cell carcinomas arise from the thin, flat cells that make up the outer layer of skin. Melanomas are more aggressive tumors that develop from pigment-producing cells called melanocytes. Melanomas can vary in appearance, but they often look like darkly pigmented masses on the surface of the skin or mucous membranes. Regardless of their appearance, all types of eyelid tumors should be evaluated by a veterinarian to determine if they are cancerous or benign.