Abstract P4-11-17: Prognostic significance of complete cell cycle arrest compared to the CPS + EG scoring system in patients with HR+/HER2- breast cancer receiving neoadjuvant chemotherapy

Abstract Background: Pathologic complete response (pCR) after neoadjuvant chemotherapy (NAC) is not predictive in HR+/HER2- breast cancer patients. Complete cell cycle arrest (CCCA) is regarded as a biomarker associated with response to endocrine therapy and recurrence-free survival (RFS). The CPS + EG scoring system has been developed and validated to predict a prognosis in patients receiving NAC. We evaluated a prognostic influence of CCCA compared to the CPS+EG score in patients with HR+/HER2- breast cancer who had residual tumors after NAC. Methods: Between January 2007 and June 2021, we retrospectively identified 1,419 HR+/HER2 breast cancer patients who underwent NAC in two academic institutes in South Korea. Among these, 918 with Ki67 index in surgical specimens with residual cancer were included. We obtained the CCCA value, which is Ki67 less than or equal to 2.7%. The clinicopathologic stage (CPS) + EG scores were obtained, and the cutoff for high risk was defined as ≥3. The primary endpoint of this study is recurrence-free survival (RFS). Results: In 918 patients, the CCCA rate was 60.1% (552/918) with a 7-year RFS of 75.8% (95% CI, 71.3-80.6%) in the CCCA group compared to 63.9% (95% CI, 58.0-70.4%) in the non-CCCA group. The group with CCCA showed significantly longer 7-year recurrence-free survival (RFS) rates compared to the non-CCCA group in both CPS + EG score-high patients (75.9% vs. 62.6%) and CPS + EG score-low patients (84.2% vs. 78.9%). In multivariable analyses, achieving CCCA was demonstrated as a prognostic factor for RFS (hazard ratio 0.488, 95% CI, 0.361-0.660) independent of stage, age, grade, and the CPS-EG score. Conclusions: Our findings show that achieving CCCA is associated with improved survival among patients with HR+/HER2- breast cancer who do not attain a pathologic complete response after NAC and suggest that a prognostic significance of CCCA is independent of the CPS-EG score. Citation Format: Sohyun Moon, Sung Gwe Ahn. Prognostic significance of complete cell cycle arrest compared to the CPS + EG scoring system in patients with HR+/HER2- breast cancer receiving neoadjuvant chemotherapy [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P4-11-17.