Quality assurance in immunohistochemistry – an update

Abstract

Introduction Diagnosis of tumours and treatment decisions for patients including breast cancer patients are based on determination of immunohistochemistry biomarkers. The accurate assessment of hormone receptor status in breast cancer and the correct classification of lymphomas is essential for appropriate patient care. The immunohistochemistry (IHC) Quality Assurance Program (QAP) includes a number of modules: diagnostic, lymphoma markers, breast markers, bright-field HER2 ISH and technical. Other countries have similar quality assurance programs. 1,2 Methods The IHC modules consist of a number of technical exercises per year with assessment of different biomarkers. The technical module evaluates different biomarkers across a range of antibodies that would be important for diagnosis of tumours. The diagnostic module allows participants to select a panel of antibodies to obtain a correct diagnosis mimicking real patient samples. The breast markers module evaluates oestrogen receptor, progesterone receptor and HER2 with a separate component for bright-field HER2 ISH testing. An audit of patient results is also performed for the breast biomarkers. The lymphoma module is used to assess markers used for classification and diagnosis of both Hodgkin’s disease and non-Hodgkin’s lymphoma. Slides are sent to participants comprising either tissue microarray blocks or composite blocks from different tissues. Homogeneity and stability testing are performed on the sections and every 20th section is stained to ensure representative tissue. Antigenic site stability is also evaluated. Slides are stained by the participating laboratory and returned for evaluation by a committee of scientists and a pathologist. Each slide is evaluated independently and an average score is returned. Each slide is scored from 0 to 5. The assessment criteria used are: • intensity of true positivity is of reasonable strength • absence of background staining (good signal to noise ratio) • sensitivity – all target tissues labelled • localisation – only target antigenic sites labelled • chromogen character – crisp and distinct • counterstain quality – complementary not obscuring • absence of artifacts • adequacy of controls – sufficiently sensitive. A score A control slide is also assessed as satisfactory, borderline or unsatisfactory. Results Participants’ results vary depending on the module being assessed and there has generally been an improvement of results over time, however deficiencies are still noticed for some biomarkers. Results of some of the modules will be presented. Discussion Immunohistochemistry is used to diagnose patients’ tumours and to determine patient treatment. Poor quality IHC will therefore have a significant impact on patient outcome. It is therefore essential that the results generated by the laboratory are accurate. External QAP forms an essential part of laboratory assessment. Participants frequently comment that the supplied material from the QAP is different to their in-house samples and that because the in-house controls worked the results are correct. This statement does not recognise the difference between Quality Control and Quality Assurance. The in-house controls, even if placed on the same slide, are Quality Controls and indicate that the antibody and the detection system are working. They do not indicate whether the result obtained is in fact correct and accurate. This is well recognised in clinical pathology where a method is validated against a reference method to determine accuracy and then QC is run internally to ensure that the reagents and instruments are working. In many cases for immunohistochemistry the controls selected are inappropriate, excessively large, show fixation variation or only reflect one level of staining. Conclusion High quality IHC results are essential to enable treating clinicians to optimise therapy for patients. The introduction and expansion of a specific quality assurance module for immunohistochemistry has enabled an ongoing assessment of the performance of biomarkers in Australia, New Zealand and South-East Asia. Despite the extraction of large amounts of information in regards to the methodology used for staining, it is usually not possible to identify one specific method that results in optimal staining although sample methods with high marks are reported. Optimisation of retrieval for a wide range of sensitivities is considered to be the important factor in achieving satisfactory results. The development of the program has resulted in an improvement in the staining quality for a number of biomarkers. Comments in this report were prepared for and on behalf of the RCPA QAP.