Oestrogen receptor (ER) expression is a prognostic and predictive marker in invasive breast cancer. Varying staining quality of immunohistochemical assays may potentially lead to misclassifications of cancers, thereby impacting therapy decisions and compromising patient safety. A recent recall notice for the anti-ER SP1 clone raised awareness about reduced staining intensity by faulty batches. Inconsistencies in antibody dilution by the vendor caused inferior SP1 performance. We analysed publicly available data from external quality assessment (EQA) programmes for ER immunohistochemistry (IHC), comprising NordiQC and the Belgian national public health institute Sciensano. IHC with the affected SP1 batches did not meet the descriptive lower limit of detection, resulting in interlaboratory performance variations and decreased EQA pass rates. We conclude that EQAs can retrospectively reveal global inferior performance of a particular clone. Additionally, the recent anti-ER SP1 clone issues highlight the importance of the use of on-slide positive controls.
Hafdallah et al. (Sat,) studied this question.