The Authors have investigated preneoplastic lesions and the problem of the identification of benign lesions considered with or without preneoplastic potential, comparing for the occasion the presence of transformation markers in these lesions with the positivity of tumor markers in neoplastic tissue. The dosages have been valued on neoplastic tissue (180 cases), dysplastic tissue (50 cases), on cystic fluid (70 cases), and on nipple discharge (80 cases). The data obtained show a marked positivity to the tumor markers and the ionic and hormonal content (K+, Na+ DHEAS, PRL evaluation). The positivity of some lesions, not properly preneoplastic (or atypical) towards some markers of neoplasia could show some differences of great interest between benignity and malignity.