Cholesterol and apolipoprotein D in gross cystic disease of the breast.

Cholesterol and apolipoprotein D (apo D) concentrations were measured in cyst fluids and sera from 66 women with gross cystic disease of the breast. Intracystic cholesterol concentrations are about twofold greater than those found in serum, whereas apo D, the major cyst fluid protein, is present in concentrations as much as 1000-fold greater than found in serum. We classified the cyst fluids into two groups by K+/Na+ ratio and albumin concentration and measured intracystic cholesterol and apo D concentrations in each group. Type I cysts had an average content of cholesterol (12.7 mmol/L) moderately lower than that in Type II cysts (17.6 mmol/L). By contrast, the average concentration of apo D in Type I cyst fluids (15.1 g/L) was slightly higher than that in Type II cysts (13.7 g/L). The absence of a correlation between cholesterol concentration and apo D concentration and the results from previous binding analysis suggest that this protein is not involved in the accumulation of cholesterol in breast-cyst fluid.