Estrogen receptor analysis in primary breast tumors by ligand-binding assay, immmocytochemical assay, and northern blot: a comparison

Estrogen receptor (ER) status is an important parameter in breast cancer ma nagement. In this study, ER protein contents established by two conventiona l techniques were confronted to ER mRNA level, to analyze whether the latte r may be introduced in routine assay. Eighty-seven breast tumor samples wer e examined. ER amounts were determined by ligand-binding assay (LBA) and by computer-assisted immunocytochemical assay (ICA), ER mRNA was analysed and quantified by northern blot. Seventy-seven percent of tumor samples examin ed were positive for ER mRNA and they all expressed the 6.7-kb receptor sig nal. No trace of small-sized ER mRNA variants was detected in any sample. F ollowing akaike information criterion (AIC) discriminant analysis, a simple linear correlation was found between ER mRNA levels and ER amounts provide d by LBA. This was not observed when either mRNA or LBA values were compare d to ICA values. These latter were found to rapidly reach a plateau at incr easing mRNA or LBA values. In conclusion, our data points to the linear cor relation between ER amounts determined in breast tumors at both protein and mRNA levels by quantitative methods; they also indicate that the semi-quan titative computer-associated ICA may complement rather than replace these q uantitative methods.