Oestrogen receptor staining of paraffin‐embedded breast carcinomas following short fixation in formalin: A comparison with cytosolic and frozen section receptor analyses

This paper describes an improved immunohistochemical method for demonstrating oestrogen receptor (OR) protein in paraffin‐embedded sections of tissue fixed for 1.5h in formalin. Thirty‐two cases of infiltrating ductal breast carcinoma were stained with a monoclonal anti‐OR antibody (H222), using a standard streptavidin–biotin method, following pretreatment with pronase. OR counts in paraffin sections were compared with those of frozen sections and with cytosolic values detcrmined by a dextran‐coated charcoal method. Twenty‐seven of the carcinomas were OR‐positive in paraffin sections. There was concordance between the paraffin section and the frozen section‐determined receptor status in 30 cases (94 per cent) and a strong correlation was observed (r = 0.76: P< 0.0001). Similarly, OR counts in paraffin sections correlated with cytosolic OR values (r = 0‐60; P < 0.001) and there was concordance in 97 per cent of cases. The percentage of positively‐stained tumour cells in paraffin sections ranged from 0 to 94 percent with staining intensities comparable to those seen in frozen sections. Staining of paraffin sections identified more OR‐positive tumours than either frozen section staining or cylosolic assay. This study validates immunohistochemical OR analysis in formalin‐fixed, paraffin‐embedded breast carcinomas using a commercial ami‐OR antibody.