Risk Factors of Response to Neoadjuvant Chemotherapy in Patients with Luminal (HER2 Negative) Breast Cancer: Roc Curve and Logistic Regression Model Results

Neoadjuvant chemotherapy (NAC) is less effective for luminal human epidermal growth factor receptor 2 (HER2) negative breast cancer (BC) patients and generally shows a low pathological complete response (pCR) after NAC compared to HER2 positive and triple negative breast cancer (TNBC). This studyaimed to determine the factors associated with histopathologic response following NAC in luminal (HER2 negative) BC.

This is a cross-sectional study conducted on 255 estrogen (ER) positive and HER2 negative BC patients after NAC between January 2018 and July 2023. Demographic and clinicopathological characteristics of the patients were collected for the statistical analysis.Chi-Square tests were used in the qualitative comparisons between study groups. Receiver Operating Characteristic (ROC) analysis was used for the diagnostic performance of Ki-67 expression and ER in determining the pCR rates. Using the Youden index, optimum cut points were determined. Also, multivariate logistic regression analysis was applied to determine the independent variables associated with the dependent variable (pCR).

After NAC, pCR was achieved in the breast in 35 (14%) patients, in the axilla in 44 (17%) patients, and in both the breast and axilla in 18 (7%) patients. Ki-67 expression was the only common variable associated with the breast, axilla and both the breast and axilla pCR. The most appropriate Ki-67 expression cut-off value for determining the breast and axilla complete response was found to be 40%. ER positivity level was only associated with pCR in the breast and the cut-off value was found to be 85%.

The results of this study raise the possibility of patients with luminal (HER2 negative) BC with Ki-67 expression higher than 40% benefiting from chemotherapy, as they showed increased pCR rates.