Leaders A scoring system for immunohistochemical staining: consensus report of the task force for basic research of the EORTC-GCCG

Accepted for publication 28 July 1997 Immunohistochemistry has become an important tool in surgical pathology, especially in the diagnosis of tumours. The demonstration of antigens more or less specific for different types of tumours has dramatically improved diagnostic accuracy. As well as being diagnostically important, the expression of several antigens as demonstrated by immunohistochemistry correlates with the prognosis of some cancers. Examples are steroid receptors in breast and gynaecological cancers,' oncogene products such as HER-2/neu in breast cancer,2 apoptosis related gene products such as bcl-2 in breast cancer,3 and cell cycle regulation proteins such as p53 (unpublished data), pRb,5 and cyclin DI in breast, and head and neck cancer.6 7 However, the initial promising results of studies on these markers could not always be confirmed. This may be because of different methodological problems. First, there may have been selection of patients and differences in treatment. Second, there are often differences in tissue processing from study to study, especially with regard to the type of antibody and the application of antigen retrieval. Third, and possibly most important, interpretation of staining and presentation of the results are not standardised resulting in low intraobserver and interobserver reproducibility. These problems are a very important obstruction for possible clinical applications. There is therefore a clear need for consensus on a protocol for scoring of immunohistochemical staining. The aim of this article is to discuss the most important items that should be part of a protocol for the scoring of immunohistochemical staining (staining patterns, tumour area to be assessed, sampling of fields of vision, scoring method, decision thresholds) and to suggest some solutions for common problems to reach a more standardised interpretation and presentation of immunohistochemical staining results. Scoring of immunocytochemical staining will not specifically be addressed, although many of the issues discussed will be applicable to cytological material. Tissue processing There are several steps in tissue processing that may influence staining patterns and intensity. These include type and duration of fixation, section thickness, antigen retrieval procedures, type and concentrations of primary, second (and third) step antibodies, and way of staining development-for example, it has recently been reported that tumour marker immunostaining intensity may be lost on stored paraffin wax slides of breast cancer.8 It is beyond the scope ofthis article to give an in depth overview of these factors, but these variables should be standardised as much as possible. Technically inadequate slides (uneven staining, uneven section thickness, heavy background) should be discarded.