Tamoxifen treatment failures in hormonally responsive breast cancers. Correlation with steroid receptors

Clinical correlation of treatment response with estrogen (ERP) and progesterone (PgRP) receptors in 81 patients revealed a remission rate of 76% if both receptors were present in the tumor. The response rate was 89% in those patients with positive receptors in whom an endocrine ablative procedure was performed and was 63% in those patients treated with tamoxifen, suggesting that the latter modality may not be effective in the treatment of some hormonally responsive tumors. An assay to determine receptor sensitivity to tamoxifen was developed and correlated with clinical response to tamoxifen treatment. Of the 56 human breast tumors analyzed, 29 tumors were ERP- and PgRP-positive and ten of these were tamoxifen-insensitive. Sixteen tumors were ERP- and PgRP-negative and tamoxifen-insensitive. Of the remaining 11 tumors, four were tamoxifen-sensitive. Nineteen of the 56 patients whose tumors were analyzed were treated for advance breast cancers with tamoxifen. Twelve patients who were ERP- and PgRP-positive and tamoxifen-sensitive responded to this modality of treatment. Seven treatment failures were noted in this group all of whom were ERP-positive and tamoxifen-insensitive. Endocrine ablation failed either prior or subsequently in three of these patients all of whom were PgRP-negative. Two patients who were ERP- and PgRP-positive and tamoxifen-insensitive subsequently responded to an alternative antihormonal treatment.