A high mitotic score in breast cancer after neoadjuvant chemotherapy is predictive of outcome and associated with a distinct morphology

Aims Neoadjuvant chemotherapy (NAC) is frequently used for the treatment of breast cancer. We sought to analyse the clinical, morphological and immunohistochemical features of tumours from patients who did not achieve pathological complete response following NAC. Methods and results We identified stage I–III post‐NAC breast cancers from surgical resections (2000–2016) with evaluable residual invasive carcinoma [ypT1a(m) or greater and ≥15% tumour cellularity]. One hundred and forty‐three tumours from 142 patients were included. On univariable analysis, a high (score 3) post‐NAC mitotic score (as compared with 1 or 2) was significantly associated with invasive ductal carcinoma (IDC) subtype (P = 0.023), high grade, pushing borders with zones of necrosis, hormone receptor and triple‐negative status, lack of hormonal therapy, higher cellularity (P