Ultrastructural characterization and biochemical profile of human gross cystic breast disease.

Human gross cystic breast disease is a benign condition affecting about 7-10% of adult women occurring with the highest incidence in the premenopausal decade. Although breast cysts do not represent a preneoplastic condition per se, several studies indicate an increased breast cancer risk in women affected by this pathology. In this report we study 115 breast cystic fluid samples obtained by needle-aspiration from women with gross cystic breast disease. The samples were analysed biochemically and the cells contained therein were observed at the electron microscope. According to their biochemical profiles, the cysts were subdivided into three types: Type I, showing a Na/K ratio < 0.5 and a typical protein content; Type II, showing a Na/K ratio >10 and a protein content quite similar to plasma; Type III, showing a Na/K ratio between 1 and 7 and an intermediate protein content. The electron microscopic examination demonstrated that Type I cystic fluid cells exhibit morphological features typical of actively synthesising and secreting cells, while the characteristics of Type II cells indicate a low metabolic activity. Type III cells have characteristics typical of both Type I and Type II cells, thereby confirming the intermediate nature of this cyst type. We hypothesise that these cyst types could represent different developmental stages of a structural evolution pathway, during which the biosynthetically active 'apocrine stage' would be the key step to cell neoplastic transformation.