BGX-Ki-67 Index as a Supplementary Marker to MIB-1 Index, Enabling More Precise Distinction Between Luminal A and B Subtypes of Breast Carcinoma and Eliminating the Problem of Membranous/Cytoplasmic MIB-1 Staining

Objectives: We compared clinical utility of MIB-1 and BGX Ki-67 clones of anti Ki-67 antibody in a group of 156 patients with invasive ductal breast cancer. Methods: MIB-1 labeling index (MIB-1LI) and BGX labeling index (BGXLI) were evaluated immunohistochemically both in primary tumors (T) and synchronous lymph node metastasis (LNM). Results: In addition to nuclear MIB-1 staining, in 23 of 145 and 19 of 144 T and LNM, respectively, membranous/cytoplasmic labeling was found In these cases, BGX Ki-67 showed exclusively nuclear labeling and presented significantly higher labeling index. High BGXLI(T) was a significant independent negative prognostic factor for disease-free survival. Moreover, based on BGXLI(T)/BGXLI(LNM), patients with high MIB-1LI(T) were stratified into low- and high-risk carriers. Conclusions: In carcinomas with membranous/cytoplasmic MIB-1 staining, additional assessment of BGXLI is recommended It may help in defining breast cancer subtype and in selection of individuals at risk who, despite appropriate therapy, would benefit from more frequent controls aimed at earlier implementation of second-line treatment.