AIM: To examine interobserver agreement in immunohistochemical evaluation of Her2 overexpression using five different antibodies on breast cancer array. MATERIAL AND METHOD: Material and method: One array was built with two cores (2 mm diameter each) from 25 breast carcinomas. Serial sections from the array were submitted to immunohistochemistry using five anti-Her2 antibodies: SP3 (NeoMarkers), HercepTest and A0485 (Dako), CB11 (Novocastra), and 4D5 (Genentech). One slide immunostained for each antibody (total = five slides) were independently scored by five observers following HercepTestTM scoring system. Interobserver agreement was evaluated in three different analysis: I (0; 1+; 2+; 3+); II (0 and 1+; 2+ and 3+) and III (0 and 1+; 2+; 3+), and the kappa statistics was applied. RESULTS: There was a good rate of interobserver agreement when the four scores were considered (0; 1+; 2+; 3+). When the scores were considered in two categories (0 and 1+; 2+ and 3+) the interobserver agreement rate was considered substantial for cases stained for SP3 and CB11, and almost perfect for cases stained for A0485, HercepTest and 4D5. For analysis III (0 and 1+; 2+; 3+), a moderate rate of interobserver agreement was considered for cases stained for CB11, and a substantial rate for other antibodies. CONCLUSION: The overall interobserver agreement was considered moderate to substantial in the evaluation of cases stained for the five antibodies. The lowest rate of agreement was obtained in the evaluation of the cases scored as weak (1+) and moderate (2+). The observers experience altered the concordance rates.
Interobserver agreement; Immunohistochemical; Her2; Breast cancer
