Retinoic acid binding proteins and steroid receptor levels in human breast cancer.

Samples of 31 human breast cancer tissues were examined for the presence or absence of cytosolic retinoic acid binding proteins (cRABP), estrogen receptors (ER) and progesterone receptors (PR). cRABP were detected as specifically sedimenting 2S components on sucrose density gradient. Specific binding under the 2S region for cRABP and under the 8S region for ERR and PR were determined. The levels of cRABP ranged from less than 1 pmol to 14 pmol per mg of cytosol protein. Tumors containing less than 3 pmol cRABP were designed as low cRABP; tissues were considered ER- and PR- when the receptor levels were less than 10 fmol/mg protein. Approximately 60% of primary and metastatic tumors examined contained high cRABP. Tumors with well differentiated histopathology exhibited increased levels of cRABP. There was no significant correlation between the presence or absence of steroid receptors and cRABP in human mammary tumors.