Antiestrogen binding sites in microsomal fractions of malignant and nonmalignant human breast tissues.

Antiestrogen binding sites (AEBS) were measured in microsomal fractions of 102 malignant breast tumors and 24 nonmalignant breast tissues. The number of AEBS was determined by Scatchard analysis. The cytosol contents of estrogen and progesterone receptors were also analyzed in these tissues. Overall, 50% of the malignant tumors and 33% of the nonmalignant normal breast tissues had detectable contents of AEBS. No correlation was observed between cytosol estrogen receptor (ER) content and microsomal AEBS in the tumors. Detailed data analysis in patients at Stage IV disease revealed that 60% of estrogen receptor positive tumors had no detectable microsomal AEBS contents whereas in the remaining 40% tumors, high affinity AEBS were observed. On the other hand, AEBS were also detected in 35% of ER-poor tumors. Anti-estrogen binding sites were higher in tumors obtained from premenopausal women than in those of postmenopausal women. The incidence of AEBS-positive tumors or AEBS concentration was not influenced by either the patients' obesity or their disease stage.