Detection of estrogen receptor in paraffin-embedded sections of breast carcinoma by immunohistochemistry and in situ hybridization.

Biopsy specimens of small breast carcinomas are often insufficient for both diagnosis and the biochemical determination of estrogen receptor (ER) protein. Recent reports from various laboratories have shown the utility of immunohistochemical detection of ER protein in paraffin-embedded tissue sections. We used immunohistochemical (IHC) staining with the Abbott ER antibody (H222) and in situ hybridization (ISH) analysis with a 35S-labeled and a biotinylated oligonucleotide probe to detect ER protein and messenger RNA (mRNA) in tissue sections of 53 breast carcinomas. The dextran-coated charcoal (DCC) assay of these same cases revealed positive receptor levels in 31 of 53 cases, whereas the IHC method was positive in 33 of 53 cases. ISH for detection of ER mRNA was more sensitive than IHC or the biochemical assay for estrogen binding proteins, as the isotopic probe detected ER mRNA in 47 of 53 cases, whereas the biotinylated probe detected ER mRNA in 46 of 53 cases. These results indicate that ER protein can be readily detected in enzyme-treated paraffin tissue sections and that the IHC detection of ER protein correlates highly with the DCC assay. ISH with isotopic and biotinylated probes detects ER mRNA in most cases found to be positive for ER protein and also in many cases without detectable ER protein. Although detection of ER protein in paraffin sections correlates highly with the biochemical assay in this report and in other reported studies, the clinical significance of increased sensitivity by ISH is unknown and must await clinical correlative follow-up studies.