Variability of predictive markers (hormone receptors, Her2, Ki67) and intrinsic subtypes of breast cancer in four consecutive years 2015-2018

Purpose Accurate monitoring of predictive markers is of utmost importance as oncological treatment decisions almost entirely depend on these factors. In this study, we conducted a quality control assessment on hormone receptors, Her2 status, Ki67 Labelling Index (LI) and histological grading in breast cancer over 4 years (2015-2018). Methods Altogether 2214 consecutive breast cancer cases were included. Data on estrogen (ER) and progesterone receptors (PR), Her2 and Ki67, were available in all cases and were tested mostly on preoperative biopsies, in selected cases on postoperative surgical specimens. ER, PR, and Ki67 were assessed with immunohistochemistry (IHC), Her2 status with IHC and fluorescence in situ hybridization. Results ER/PR were positive in 74-79% cases, ER/PR/Her2 negative in 6.16-10.70% and Her2 positive in 11.49-13.88%/year. Ki67 had median values as 15-17.5% in ER/PR-positive cases, 55-60% in triple-negative cases and 30-32.50% in Her2-positive cases. Histological grading distribution for well (G1), moderately (G2) and poorly (G3) differentiated carcinomas was 15.8-19.1% for G1, 54.2-54.8% for G2 and 21.7-23.7% for G3 cases. Variation in yearly distributions was not significant in any of these markers. Conclusions Predictive markers displayed a yearly similar distribution in breast cancer cases independently of grading or of intrinsic subtypes. These results point to a qualitative high performance of predictive marker assessment in breast cancer, corresponding to expected on average positivity rate per marker and per year. It is recommended to monitor positivity rate of ER, PR, Ki67 and Her2 yearly or periodically to comply with quality assurance requirements.