PGR and neoplasm: Notably, even in single-analyte assays such as the routinely-used immunohistochemical (IHC) assessment of oestrogen receptor (ER) or progesterone receptor (PR), the assays present a performance challenge as is reflected in studies demonstrating considerable inter-laboratory variability in IHC-based ER evaluation (especially with respect to detecting ER-positive tumours with low ER positivity) [2–3].