Neoadjuvant Chemotherapy and Pathologic Complete Response in HR+/HER2- Breast Cancer: Impact of Tumor Ki67 and ER...

Neoadjuvant chemotherapy (NAC) is extensively employed in breast cancer (BC), primarily for aggressive subtypes like triple-negative and human epidermal growth factor receptor 2 (HER2)-positive BC and in estrogen receptor-positive (ER+)/HER2- BC with high-risk features. In ER+/HER2- BC, pathological complete rates are much lower (<10%), while axillary dissection rates are higher. This study focuses on hormone receptor-positive (HR+)/HER2- BC patients undergoing NAC, examining its impact on pathological complete response (pCR) rates, with specific attention to tumor Ki67 and ER status.

Retrospective data analysis from Kartal Dr. Lütfi Kırdar City Hospital included HR+/HER2- BC patients who received NAC. Clinicopathological factors, NAC response, and surgical outcomes were assessed. Statistical analyses evaluated the association between Ki67, ER status, and pCR.

Of 203 patients, 11.8% achieved pCR. Ki67 (p < 0.001) and ER percentage (p < 0.001) significantly correlated with pCR. Higher Ki67 was associated with increased pCR likelihood (HR: 1.03, 95% CI: 1.01-1.05). A Ki67-pCR probability curve revealed a cutoff of 23.5%. ER%-pCR analysis showed decreasing pCR rates with higher ER percentages. Multivariate analysis confirmed Ki67 (p = 0.003, HR: 1.02) and ER percentage (p = 0.019, HR: 0.97) as independent predictors of pCR probability.

Consideration of Ki67 and ER percentage aids in NAC decisions for HR+/HER2- BC, identifying patients with high NAC response rates, facilitating axillary preservation, and potentially avoiding axillary dissection. The pCR rates in patients with Ki67 ≤24 are particularly low, especially in patients with a high ER percentage. In these cases, upfront surgery and adjuvant treatment should be considered instead of NAC.