Interobserver Variation in the Assessment of Immunohistochemistry Expression Levels in HER2-Negative Breast Cancer: Can We Improve the Identification of Low Levels of HER2 Expression by Adjusting the Criteria? An International Interobserver Study

Ximena Baez-Navarro^*, Mieke R. van Bockstal, Diënna Nawawi, Glenn Broeckx, Cecile Colpaert, Shusma C. Doebar, Marieke C.H. Hogenes, Esther Koop, Kathleen Lambein, Dieter J.E. Peeters, Renata H.J.A. Sinke, Johannes Bastiaan van Brakel, José van der Starre-Gaal, Bert van der Vegt, Koen van de Vijver, Celien P.H. Vreuls, Willem Vreuls, Pieter J. Westenend, Carolien H.M. van Deurzen