Estrogen receptor protein. Stability of 8S molecular form in frozen cytosols and practical criteria for its confirmation.

Estrogen receptor has been used in determining the efficacy of endocrine therapy in mammary tumors. Complete study of a tumor usually requires two procedures, a dextran-coated charcoal method for measuring binding capacity and binding affinity and a sucrose density procedure for confirmation of 8S protein, both of which are time consuming and expensive. A stability study of the 8S and 4S molecular forms in frozen cytosols at 24 hours, 48 hours, and one week was conducted. Some loss of these, forms after storage was evident, but in all cytosols studied, the two distinct forms could still be identified. Using a group of 100 tumor samples analyzed by both methods, practical criteria for determining when the 8S molecular form should be confirmed by a sucrose density gradient on the frozen cytosol have been formulated.