[Evaluation of pathological response to neoadjuvant chemotherapy in breast cancer: correlation with molecular phenotype].

Introduction And Objective: Breast cancer can be classified into different molecular subtypes with important therapeutic and prognostic implications. Neoadjuvant chemotherapy (NAC) increases the possibility of performing conservative surgery and allows in vivo testing of the sensitivity of the tumor. Our aim was to evaluate the pathological response to NAC in relation to the molecular phenotype and the different definitions of the pathological response.

Patients: 228 patients treated with NAC and subsequent surgery between 2012 and 2018 were selected from our breast cancer database. Molecular phenotypes were established based on the criteria of the St Gallen 2013 Conference. Pathological response was evaluated following Miller-Payne (breast) and Sataloff (axilla) classification systems.

Results: The most frequent molecular phenotype was luminal B/HER2 negative (30.3%), followed by luminal B/HER2 positive (26.3%), triple negative (24.6%), HER2 positive (13.2%), and luminal A (5.7%). The rate of pathological complete response (pCR) was 35.5% in breast and 15.3% in axilla. The rate of pCR considering breast and axilla together was 26.8%. The molecular phenotype with the highest rate of pCR was HER2 positive (66.7%) followed by triple negative (30.4%), luminal B/HER2 positive (21.7%), luminal B/HER2 negative (14.5%), and luminal A (7.7%) (p < 0.001). The same results were found with the different definitions of pCR we evaluated.

Conclusions: Complete pathological response to NAC in breast cancer depends largely on the molecular phenotype of the tumor, regardless of the definition of pCR, with the highest response rates in the breast and axilla in the HER2 positive and triple negative phenotypes.