Breast Cyst Fluid Proteins and Breast Cancer

A specific breast cyst fluid protein was purified by the following steps: ultracentrifugation, gel filtration, DEAE and Con A chromatography, and gel filtration with guanidine, 6 M. The protein was pure, having a molecular weight of 17,800 daltons on SDS-PAGE and 68,000 daltons on gel filtration. The GCDFP 17,800 is immunologically distinct from other breast cyst fluid components and known milk and plasma proteins. A specific radioimmunoassay was developed and used to determine GCDFP 17,800 in 158 samples of breast cancer cytosol. The GCDFP 17,800 levels were significantly different between grade I tumors (mean of 813 ng protein per mg +/- 430 SEM) and grade III tumors (mean 184 ng protein per mg +/- 59 SEM) and were correlated with progesterone receptor values in postmenopausal women (Spearman's correlation, p = 0.03) but not in premenopausal women. The value of GCDFP 17,800 did not differ between the pre- and the postmenopausal women. By immunocytochemistry the intracellular localization of the GCDFP 17,800 was also found in relation to tumor grading and in correlation with PR values. GCDFP 17,800 appears as a hormone-induced protein of the breast cells. Its intracellular detection by means of radiolabeling allows a more sensitive and precise evaluation of the hormone-dependence of the breast cancer cells and emphasizes the heterogeneity of the tumor cell population.