Women with locally advanced breast cancer who have achieved a pathological complete response (pCR) after neoadjuvant chemotherapy (NCT) have significantly better survival than those not obtaining a pCR. Identifying certain prognostic factors for patients who had not reached pCR is important because fractions of this population might benefit from other new adjuvant treatments. High Ki67 expression, a nuclear
marker of breast carcinoma cell proliferation, in remnant disease after NCT has been described as a poor prognostic factor.
             This study aimed to assess post-neoadjuvant chemotherapy Ki67 index expression and estrogen receptor (ER) status on residual tumour; moreover, we attempted to elucidate the possible correlations between disease-free-survival (DFS) and overall survival (OS) as a function of these two parameters in a retrospective group of 184 women with locally advanced breast cancer stage IIB-IIIC, treated with NCT who had not obtained pCR and underwent surgery. We also analyzed the relationship between the expression levels of Ki67 (≥15%, <15%) and the clinical response, the histological types, the histopathological grades of the tumours as well as the lymph node involvement status in these patients from Hospital University Cancer Centre of Sidi-Bel-Abbes (west of Algeria). The median patients' age was 47years (27-81). Post-chemotherapy Ki67 index expression correlated directly with clinical response. The mean Ki67 expression value after NCT was significantly higher in patients with negative clinical responses than in those who developed objective responses (p=0.013). Univariate analysis of post-chemotherapy Ki67 expression levels as function of pathological tumour characteristics showed a significant difference for histopathological type (p = 0.025) and lymph node involvement status (p = 0.04). Patients' median follow-up was 23.5 months. Positive post-chemotherapy ER was associated with significantly higher 5-year DFS (p=0.006). Survival analysis conducted as function of Ki67 thresholds, confirmed a significantly shorter DFS and OS in patients with Ki67 expression ≥15%, following NCT compared with patients with low (<15%) Ki67 expression (p = 0.033 and p = 0.002, respectively). Based on patients' outcomes, the OS and DFS rates were improved in patients with lower Ki67 levels. The 5-year DFS was significantly worse in tumour with negative post-treatment estrogen receptors. A prognostic model could be formulated based on both the Ki67 index and ER