IMMUNOHISTOCHEMICAL DETERMINATION OF ESTROGEN-RECEPTOR - COMPARISON OF DIFFERENT METHODS OF ASSESSMENT OF STAINING AND CORRELATION WITH CLINICAL OUTCOME OF BREAST-CANCER PATIENTS

Immunohistochemical staining for oestrogen receptor (ER) has been carr ied out using antibody ER ID5 on 170 women who received first-line tam oxifen treatment for evaluable metastatic breast cancer. ER status had been determined some years previously, using a ligand-binding cytosol assay. The adequacy of the tissue used for the cytosol assay was alwa ys checked by histology on an adjacent block and was deemed to be typi cal of the tumour overall as was the block used for immunohistochemist ry. Six different methods were used to assess the degree of staining a nd comparisons were made to determine which method gave the most clini cally relevant results. Clinical outcome was assessed both in terms of duration of response to tamoxifen determined by log-rank analysis and type of response using the chi-squared test. The ER immunohistochemic al assay gave superior results compared with the cytosol assay, with a ll of the subjective methods of assessment of staining giving statisti cally significant correlations with clinical outcome. The additional c ontribution of progesterone receptor (PR) staining with antibody NCL P GR was also studied.