Tonsil surface epithelium is ideal for monitoring Ki-67 immunohistochemical staining

Aims To identify an easily obtainable non‐neoplastic tissue that can be used as control material for monitoring optimal Ki‐67 immunohistochemical staining. Methods and results Various tissues, including tonsil (60), uterine cervix (31), breast skin (26), oesophagus (15), stomach (15), small intestine (15) and colon (16), were studied in the search for ideal control tissue. Tonsil surface epithelium is superior to other tissues because it displayed an easily recognized Ki‐67 staining pattern including high positive (parabasal layer), low positive (intermediate layer) and negative (basal and superficial layers) zones. Moderate to weak staining of the majority of the intermediate cells could serve as a threshold for positive staining. Of the variables potentially affecting staining results that were tested, the pretreatment solution for antigen retrieval had the greatest impact, of which pH 9 EDTA was far better than pH 6 citrate solution. Conclusions Tonsil surface epithelium is a useful control for monitoring Ki‐67 staining. Achieving optimal staining results could minimize variations in Ki‐67 index due to differences in the staining methods used by different laboratories.