GCDFP-70 protein in cyst fluid identified as albumin and used to classify cysts in women with breast gross cystic disease.

We used sodium dodecyl sulfate-polyacrylamide gel electrophoresis to study cyst fluids from women with breast gross cystic disease. The subjects could be classified into two categories according to the concentrations of protein GCDFP-70 in the cyst fluid: those with Type I cysts had a very low content of this protein; those with Type II cysts had very high concentrations. Analysis of the amino acid sequence of GCDFP-70 from both cyst fluid types confirmed that this protein is human plasma albumin. The average concentration of albumin found in Type I cyst fluids was 0.32 g/L and that corresponding to Type II was 10.16 g/L. Thus, albumin quantification from cyst fluids or analysis by either polyacrylamide or agarose gel electrophoresis provides a simple procedure for classifying these fluids, yielding results that correlate well with previous classifications based on other measurements such as sodium, potassium, and chloride concentrations. This albumin-based quantification method may improve the classification of breast cysts and might be useful in further studies on functional changes in the cysts and their relationship to breast cancer.