Predictive Value of IHC4 Score for Pathological Response to Neoadjuvant Chemotherapy in Hormone Receptor-Positive Breast Cancer

Purpose: This study aimed to explore the value of IHC4 in predicting pathological response after neoadjuvant chemotherapy in patients with hormonal receptor (HR)-positive breast cancer (BC). Materials and Methods: In this retrospective exploratory study, data for 68 HR-positive BC patients who received neoadjuvant chemotherapy were recorded. IHC4 scores were calculated based on estrogen receptors/progesterone receptors, Ki-67 and HER2 status. Logistic and ordinal regression analyses in addition to likelihood ratio test were used to explore associations of IHC4 scores and other clinico-pathological parameters with pathological complete response (pCR) and pathological stage. Results: Taking the 25th percentile as the cut-off, a lower IHC4 score was associated with an increased probability of pCR (low; 52.9% vs. High; 21.6%, OR=4.1, 95% CI=1.28-13.16, p=0.018) and a lower pathological stage (OR=3.9, 95% CI=1.34-11.33, p=0.012). When the IHC4 score was treated as a continuous variable, a lower score was again associated with an increased probability of pCR (OR=1.010, 95% CI=1.001-1.018, p=0.025) and lower pathological stage (OR=1.009, 95% CI=1.002-1.017, P=0.008). Lower clinical stage was associated with a better pCR rate that was of borderline significance (P=0.056). When clinical stage and IHC4 score were incorporated together in a logistic model, the likelihood ratio test gave a P-value of 0.004 after removal of the IHC4 score and 0.011 after removal of the stage, indicating a more significant predictive value of the IHC4 score for pCR. Conclusions: This study suggests that the IHC4 score can predict pathological response to neoadjuvant chemotherapy in HR-positive BC patients. This finding now needs to be validated in a larger cohort of patients.