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.