Correlation between numerical and categorical immunohistochemical score of Ki-67 and HER2 with clinicopathological parameters of breast cancer

Aim To evaluate the relationship between numerical and categorical immunohistochemical score of Ki-67 and human epidermal growth factor of receptor 2 (HER2) with clinicopathological parameters of breast cancer (BC). Methods The study included 311 patients with invasive BC diagnosed at the Department of Pathology, School of Medicine in Sarajevo, Bosnia and Herzegovina, during the period 2015-2019. The expression level of Ki-67 and HER2 was detected by immunohistochemical analysis. Results The expression of Ki-67, as a numerical variable correlated significantly with tumour grade (p=0.025), progesterone receptor (PR) (p=0.034) and categorical score of HER2 (p=0.028). When Ki-67 was categorized into high (>14%) and low (≤14%) level groups, a statistically significant association was found between Ki-67 level groups and HER2 status (categorical and numerical) (p=0.001 and p=0.043, respectively), as well as significant negative linear correlation with PR (p=0.037). The expression of HER2, as a numerical variable, showed a statistically significant correlation with tumour grade (p=0.038), PR (p=0.025) and categorical Ki-67 (p=0.043). Categorical score of HER2 correlated significantly with age (p=0.025), histologic type (p=0.039), tumour grade (p=0.016), estrogen receptor (ER), (p=0.002) progesterone receptor (PR) (p=0.0001), and categorical and numerical value of Ki-67 (p=0.0001 and p=0.0001, respectively). Conclusion The results demonstrated that the categorical immunohistochemical score of HER2 provided a greater association with clinicopathological parameters than numerical score of BC. Furthermore, a slightly better correlation with clinicopathological parameters was shown by the numerical value than by the categorical score of Ki-67 by applying a cut-off value of 14%