The predictive role of Ki67 in pathological complete response (pCR) and invasive disease-free survival (IDFS) in HER2-positive breast cancer: A retrospective study of 246 cases.

person Laura Weydandt Department of Gynecology, Medical Center, University of Leipzig and Department of Gynecology and Obstetrics, University Carl Gustav Carus, Technical University Dresden, Leipzig, Dresden, Germany info_outline Laura Weydandt, Saida Agabejli, Massimiliano Lia, Pauline Wimberger, Bahriye Aktas, Theresa Link

Authors person Laura Weydandt Department of Gynecology, Medical Center, University of Leipzig and Department of Gynecology and Obstetrics, University Carl Gustav Carus, Technical University Dresden, Leipzig, Dresden, Germany info_outline Laura Weydandt, Saida Agabejli, Massimiliano Lia, Pauline Wimberger, Bahriye Aktas, Theresa Link Organizations Department of Gynecology, Medical Center, University of Leipzig and Department of Gynecology and Obstetrics, University Carl Gustav Carus, Technical University Dresden, Leipzig, Dresden, Germany, Department of Gynecology and Obstetrics, University Carl Gustav Carus, Technical University Dresden, Dresden, Germany, Department of Gynecology, Medical Center, University of Leipzig, Leipzig, Germany Abstract Disclosures Research Funding No funding sources reported Background: While Ki67 is a routine diagnostic measure for early hormone receptor positive breast cancer, it is not integrated into the standard procedure for patients with Human Epidermal Growth Factor Receptor 2 (HER2)-positive breast cancer patients, given the substantial risk linked to HER2 expression alone. Consequently, the predictive significance of Ki67 in achieving pathological complete response (pCR) or invasive disease-free survival (IDFS) in this subgroup remains uncertain. Methods: This retrospective, bi-centric analysis focused on HER2-positive early breast cancer patients undergoing neoadjuvant chemotherapy from 2015 to 2023. We assessed the correlation between Ki67 values and the achievement of pathological complete response (pCR, defined as ypT0/is, pN0). Multivariable logistic regression analyzed the independent association of various clinical parameters, including Ki67, with pCR. Ki67 values were categorized into risk groups (low <15%, intermediate 15.1-35%, high >35%) following the GepardTrio data [1]. Kaplan-Meier estimator calculated differences in overall and invasive disease-free survival. Results: The study included 246 HER2-positive early breast cancer patients with known Ki67 expression, followed for a median of 42 months. The median age was 52 years. Final nodal status was pN0 in 80.5%, pN1 in 15%, and pN2 in 3.3%. Hormone receptor positivity was observed in 66% of patients. 147 patients (60%) achieved pCR. Median Ki67 was 30. When categorized, 13% were low, 41.5% intermediate, and 45.5% high risk. No correlation between Ki67 and pCR was observed (p=0.25). HER2 IHC score 3+ significantly increased pCR compared to IHC 2+ (62.2% vs. 44.6%, p=0.023). Hormone receptor-positive tumors had a lower pCR rate (52.7% vs. 72.4%, p=0.0016. 5-year overall survival was 96.5% for pCR and 83.8% for non-pCR (p=0.008). 5-year invasive disease-free survival showed no difference between low Ki67 (89.5%), intermediate Ki67 (79.9%), and high Ki67 (80.9%) groups (p=0.77). Conclusions: In this study, Ki67 did not predict pCR in HER2-positive breast cancer, providing no additional clinical value. HER2 IHC score and hormone receptor status were predictive indicators for pCR. Ki67 expression appears to lack additional value in HER2-positive breast cancer, considering resource implications. 1. Denkert C et al: Ann Oncol. 2013 Nov;24(11):2786-93. doi: 10.1093/annonc/mdt350. Epub 2013 Aug 22. PMID: 23970015.