Validity and Reproducibility of Immunohistochemical Scoring by Trained Non-Pathologists on Tissue Microarrays.

Background: Scoring of immunohistochemistry (IHC) staining is often done by non-pathologists, especially in large-scale tissue microarray (TMA)-based studies. Studies on the validity and reproducibility of scoring results from non-pathologists are limited. Therefore, our main aim was to assess interobserver agreement between trained non-pathologists and an experienced histopathologist for three IHC markers with different subcellular localization (nucleus/membrane/cytoplasm). Methods: Three non-pathologists were trained in recognizing adenocarcinoma and IHC scoring by a senior histopathologist. Kappa statistics were used to analyze interobserver and intraobserver agreement for 6,249 TMA cores from a colorectal cancer series. Results: Interobserver agreement between non-pathologists (independently scored) and the histopathologist was "substantial" for nuclear and membranous IHC markers (K_range= 0.67-0.75 and K_range= 0.61-0.69, respectively), and "moderate" for the cytoplasmic IHC marker (K_range= 0.43-0.57). Scores of the three non-pathologists were also combined into a "combination score" (if at least two non-pathologists independently assigned the same score to a core, this was the combination score). This increased agreement with the pathologist (K_nuclear = 0.74; K_membranous = 0.73; Kcytopasmic = 0.57). Interobserver agreement between non-pathologists was "substantial" (K_nuclear = 0.78; K_membranous = 0.72; Kcytopasmic = 0.61). Intraobserver agreement of non-pathologists was "substantial" to "almost perfect" (K_nuclear,range = 0.83-0.87; K_membranous,range = 0.75-0.82; Kcytopasmic = 0.69). Overall, agreement was lowest for the cytoplasmic IHC marker. Conclusions: This study shows that adequately trained non-pathologists are able to generate reproducible IHC scoring results, that are similar to those of an experienced histopathologist. A combination score of at least two non-pathologists yielded optimal results. [ABSTRACT FROM AUTHOR]