Immunohistochemical expression of hormone receptors and the histological characteristics of biochemically hormone receptor negative breast cancers

Background  Most of the discordant cases between biochemical and immunohistochemical (IHC) assays for hormone receptor (HR) status in breast cancers are due to negative findings from the biochemical assay but positive IHC findings. However determining HR status based on IHC only in biochemically HR negative breast cancers has never been studied. The aim of this study is to examine the histological characteristics in immunohistochemically HR positive but biochemically HR negative breast cancers. Methods  IHC staining for HRs in 345 biochemically HR-negative breast cancers was done. The relationship between HR status by IHC and the histological characteristics was assessed. Results  In 345 cancers, 105 (30.4%) were estrogen receptor- (ER) or progesterone receptor- (PR) positive by IHC. The enzyme-immunoassay (EIA) HR titer was higher in immunohistochemically HR-positive tumors (ER: 2.7 fmol/mg protein; PR: 0.8 fmol/mg protein) than in negative tumors (0.6 fmol/mg protein in both HRs). IHC-assessed ER positivity on histological sections was high in some tumor types, such as mucinous carcinoma (77.8%), invasive micropapillary carcinoma (66.7%), and infiltrating ductal carcinoma of no special type with abundant stroma (60.2%). Among infiltrating ductal carcinomas of no special type, low nuclear grade tumors were all ER positive and high nuclear grade tumors showed low ER positivity by IHC, even in biochemically HR negative cancers. Conclusion  The IHC-assessed HR status may reflect tumor cell behavior, such as overall and disease-free survival and endocrine response, better than HR status as assessed by the enzyme-immunoassay method. Immunohistochemically HR-positive but biochemically HR-negative breast cancers include infiltrating ductal carcinomas of no special type with low nuclear grade and some tumor types with high stromal content. We can assess the true HR status by IHC especially these tumors.