ESTROGEN-RECEPTOR IMMUNOHISTOCHEMISTRY IN FORMALIN-FIXED, PARAFFIN-EMBEDDED BREAST-TUMOR TISSUE - ENHANCED SENSITIVITY USING A MONOCLONAL ANTIBODY COCKTAIL

To investigate whether the immunohistochemical estrogen receptor (ER) assay could be improved with the use of a cocktail of anti-ER monoclon al antibodies (clones 1D5 and LH1), we compared such a cocktail with e ach of its constituent antibodies acting alone, on formalin-fixed, par affin-embedded sections from 56 cases of breast carcinoma and with the Abbott ER-ICA acting on frozen sections from the same tissues. The la tter was considered to be the standard reference in this study. With a 90 min fixation, the cocktail showed enhanced reactivity over that of single antibodies, exhibiting a 98% sensitivity and 100% specificity when compared with the reference ER-ICA assay (sensitivity designated 100%). In addition, the effect of overfixation on the immunoreactivity of the cocktail and of the single antibodies was evaluated in tissues fixed for 1, 3, or 7 days. Overfixed tissues exhibited diminished rea ctivity with all antibodies. The ER-cocktail, ER-IDS and ER-LH1 showed a 20, 26, and 35% reduction in reactivity, respectively, with the lon ger fixation time. When more vigorous epitope retrieval methods were u sed, ER-cocktail reactivity was almost completely recovered (to 97%), while the reactivities ER-1D5 and ER-LH1 were recovered to lesser exte nts (87 and 81%, respectively), We found that the ER-cocktail produced the highest specific nuclear staining with no increased background st aining. We conclude that an ER-cocktail as used in these studies could , to advantage, replace the single antibodies currently used for ER im munohistochemical assays.