Measurement of estrogen receptor status by immunocytochemistry in paraffin wax sections

The estrogen receptor (ER) status and, to a lesser extent, progesterone receptor status have been recommended by recently published guidelines as important for routine prognostic and predictive evaluation of breast cancer. Although the clinical utility of ER status has been largely validated using biochemical ligand-binding assays such as the dextran-coated, charcoal ligand-binding assay, there has been the need to develop the ER immunocytochemical assay as a more accurate and practical alternative. In particular, ER status as determined on paraffin sections by immunocytochemical assay has been shown to be superior to the ligand-binding assay for predicting response to adjuvant endocrine therapy in breast cancer. The success of the paraffin-section assay is founded on two principles. The first relates to the advent of the heat-mediated, antigen-retrieval technique capable of restoring ER and progesterone receptor antigenicity in routinely prepared diagnostic formalin-fixed, paraffin-embedded tissue sections. The second is associated with the capacity for this substrate to provide more reliable and reproducible semiquantitative assessment of ER status in morphologically better-preserved tissue used routinely for histopathological diagnosis. The aim of this chapter is to describe the methodology currently used for optimal reproducible demonstration, scoring, and assessment of ER status in paraffin wax-embedded tissue sections in relation to the management of breast cancer in a routine or clinical-trial setting.