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The role of Ki67 as a predictive biomarker for pathologic complete remission (pCR) in patients with HER2 positive early breast cancer (BC) receiving neoadjuvant chemotherapy (NACT) in combination with trastuzumab and pertuzumab
Nada M.1, Kolberg-Liedtke C.2, Krajewska M.2, Bittner A.-K.3, Hannig C.V.4, Petzel A.2, Bankfalvi A.3, Wetzig S.1, Kolberg H.-C.1
1Marienhospital Bottrop, Bottrop, Deutschland, 2Charité - Universitätsmedizin Berlin, Berlin, Deutschland, 3Universitätsklinikum Essen, Essen, Deutschland, 4Onkologische Gemeinschaftspraxis Bottrop, Bottrop, Deutschland

Introduction: Ki67 is established as a prognostic and predictive biomarker in early BC. Although the prognostic and predictive values are most relevant in hormone receptor (HR) positive HER2 negative patients, they have also been demonstrated in triple negative and HER2 positive cases. However, there are limited data regarding Ki67 as a predictor of pCR in HER2 positive patients treated with NACT in combination with trastuzumab and pertuzumab.
Methods: We identified patients in our database who received NACT for HER2 positive BC after approval of pertuzumab in Germany. Patients who received only trastuzumab and patients treated in clinical studies were excluded, leaving only those patients who had received neoadjuvant chemotherapy in combination with trastuzumab and pertuzumab. The association between Ki67 and pCR (ypT0 and ypN0 or ypTis and ypN0) was calculated by univariate logistic regression.
Results: 33 patients were included with regard to the criteria mentioned above. 24 of those 33 (72.7%) patients achieved a pCR. Of all the parameters analyzed (age, tumor size, nodal status, grade, HR status and Ki67) only Ki67 was significantly associated with pCR (p=0.039). Median Ki67-values for non pCR and pCR were 20% (SD: 10%, 25%) vs. 55% (24%, 71%), respectively.
Conclusion: Our analysis underscores that Ki67 is a strong predictive biomarker regarding pCR after NACT combined with trastuzumab and pertuzumab. Due to the small sample size in our study we were not able to define a cut-off. However, among several other established biomarkers Ki 67 was the only parameter showing a significant association with pCR.