Improving Prognosis of Surrogate Assay for Breast Cancer Patients by Absolute Quantitation of Ki67 Protein Levels using Quantitative Dot Blot (QDB) Method

Abstract

Background: Immunohistochemistry (IHC) based-surrogate assay is the prevailing method in daily clinical practice to determine the necessity of cytotoxic therapy for Luminal-like breast cancer patients worldwide. It relies on Ki67 scores to separates Luminal A-like from Luminal B-like breast cancer subtypes. Yet, IHC method is plagued with subjectivity and inconsistency. We attempted to circumvent these issues by measuring Ki67 levels absolutely, quantitatively and objectively.Methods: The Ki67 protein levels in a cohort of 253 specimens were measured with IHC and Quantitative Dot Blot (QDB) methods respectively, and used to assign these specimens into Luminal A-like and Luminal B-like subtypes accordingly. Their performances were compared with the Kaplan-Meier, univariate and multivariate survival analyses of the overall survival (OS) of Luminal-like patients.Results: The surrogate assay based on absolutely quantitated Ki67 levels (cutoff at 2.31 nmole/g) subtyped the Luminal-like patients more effectively than those based on Ki67 scores (cutoff at 14%) (Log rank test, p=0.00052 vs p=0.031). It is also correlated better with OS in multivariate survival analysis [Hazard Ratio (HR) at 6.89 (95%CI: 2.66-17.84, p=0.0001) vs 2.14 (95%CI: 0.89-5.11, p=0.087)].Conclusions: Our study showed the performance of surrogate assay may be improved significantly by measuring Ki67 levels absolutely, quantitatively and objectively.