Non-lactating mastitis is generally not cancerous. Non-lactating mastitis is an inflammatory condition that occurs during the non-lactating period and can be broadly categorized into two main types: ductal dilatation and granulomatous mastitis. Ductal dilatation, also known as periductal mastitis or plasma cell mastitis, is often caused by a bacterial infection, and the inflammation is thought to be centered in the areola and is more closely related to the large ducts behind the areola. Depending on the stage and period of the disease, anti-infective and surgical treatments are the mainstay of treatment. Granulomatous mastitis, also known as lobular mastitis, is an autoimmune disease caused by hypersensitivity to breast milk. Most of the lumps are peripheral, and hormone therapy and surgery are the main treatments. So non-lactating mastitis is not cancerous.