A mass in the mammary gland, either mobile or immobile. once the mass has reached the size of a small garden pea, it can be detected by palpation. with mammography a larger number of early breast cancers are being detected since this techniques allows detection prior to the point at which the mass can be felt. breast masses are not always malignant. benign fibrocystic breast disease is not uncommon. a fine needle biopsy aspiration can distinguish a cystic mass from a solid one.