Mammary gland tumors are the third common type of cancer in older female cats, with the most common symptom manifesting as a lump in the breast tissue.[1] Domestic short-haired cats and Siamese appear to have a higher incident rates.[2] The tumor is typically firm and nodular, and adheres to the overlying skin.[3] Nipples may also appear to be red and swollen, oozing yellowish fluid.[11]