RESUMO
Background & objectives: Breast cancer is the most common cancer of women. Inferior prognosis in some patients has been attributed to the higher proliferative capability of the tumour. Immunohistochemistry (IHC) for Ki-67, despite being a simple and cost-effective method, has not become a valid tool to evaluate this biomarker. This is ascribed to variation in pre-analytical and analytical techniques, variable expression, hotspot distribution and inter-and intra-observer inconsistency. This study was aimed at defining the analytical and clinical validity of real-time quantitative polymerase chain reaction (RT-qPCR) as an alternative to IHC evaluation. Methods: This study included a total of 109 patients with invasive breast cancers. Ki-67 IHC visual assessment was compared with the mRNA value determined by RT-qPCR. Concordance between both the methods was assessed. Receiver operating characteristic (ROC) curve analysis and Cohen's kappa value with intraclass correlation were performed. Results: The threshold value for Ki-67 by RT-qPCR obtained by ROC curve was 22.23 per cent, which was used to divide breast cancer cases into high proliferative and low proliferative groups. A significant correlation was observed between both the breast cancer groups formed using RT-qPCR threshold as well as median laboratory value of Ki-67 labelling index by IHC. Interpretation & conclusions: The study results showed a significant correlation between the two methods. While IHC is subject to technical and interpretative variability, RT-qPCR may offer a more objective alternative.