Supplementary Material for: Hormone receptor and HER2 status switch in non-pCR breast cancer specimens after neoadjuvant therapy

(1) Introduction: This project aimed to identify the frequency of a switch of hormone receptor (HR) and/or HER2 status after neoadjuvant chemotherapy (NAC) for early breast cancer.
(2) Methods: Tumor samples from patients without pathological complete response (non-pCR) were evaluated. Pathological complete response (pCR) was defined as no invasive tumor in breast and lymph nodes (ypT0/is ypN0). HR and HER2 status determined before NAC was compared with the corresponding receptor status determined in the surgical specimen after NAC. (3) Results: 245 consecutive patients with primary invasive breast cancer, treated with NAC with/without targeted therapy between January 1st, 2016 and December 31st, 2019, at the LMU breast center, Munich, Germany, were identified. In 128 patients (52 %), surgery revealed non-pCR after completed NAC. In 35 cases (27 %), a switch of either HR and/or HER2 status between the initial biopsy and the surgical specimen was detected. 20 cases had a switch in HR status, while 15 cases had a switch in HER2 status. (4) Conclusion: In a substantial number (27 %) of non-pCR cases, a switch in biomarker status after completed neoadjuvant treatment was detected. These results are consistent with prior evidence. Yet, routine re-evaluation of HR and HER2 status is not recommended in guidelines so far. Future research needs to address the impact of HR and HER2 status switch on therapy adaptation and on subsequent patient outcome. Particularly, in view of the recent therapy advances, it will be critical to evaluate whether individualization of treatment concepts based on the biology of the non-pCR specimens is preferable to the initial therapy concept based on the pathology at primary diagnosis.