The biochemistry of breast cyst fluids and duct secretions.

The ratio of potassium to sodium concentrations in breast fluids has led other investigators to the subclassification of cysts into two types: 1) apocrine (secretory) cysts with high potassium and low sodium, and 2) attenuated (flattened) cell cysts with low potassium and high sodium content. Apocrine cells are thought by some to actively secrete potassium. Cell typing is considered important as apocrine cysts are more likely to be bilateral, multiple, recurrent, and serve as markers for epithelial cell atypia. A retrospective study of the biochemical analyses of 58 cyst fluids and 28 duct secretions obtained by nipple aspiration was conducted. Potassium and sodium concentrations obtained from 12 cyst fluids were statistically correlated with creatinine concentrations. Evidence is presented indicating that micro cysts are initially apocrine in cell type and are more likely in continuity with the terminal ductal-lobular unit. It is postulated that apocrine cysts undergo cellular desquamation and lysis, becoming attenuated cysts. The ratio of potassium to sodium is altered by cell degradation rather than active secretory processes. Biochemical contents of cysts and nipple aspiration fluids are compared.