Objectives We aimed to evaluate the cut-off value of Ki67 that predicted survival in luminal breast cancer and investigated its survival impact according to axillary lymph node involvement.

Methods We retrospectively selected 321 cases of histologically confirmed, early stage, breast cancer treated between 2011–2015. All patients had ER and/or PR positive (>10% expression) and HER2- tumors. We evaluated the prognostic value of several cut-off levels of Ki67 in terms overall survival (5-year OS): 14%, 20%, 30% and 50%. We also considered different subgroups according to axillary lymph node involvement: pN0(38%), 1–3pN+(35%) and ≥4pN+(27%). We used Kaplan Meier method and Cox regression models to evaluate survival.

Results Median age was 49 years-old, 42% were menopausal. Media Ki67 was 28%. Sixty four percent of patients had mastectomy, 93% received chemotherapy and 88% radiation therapy. On overall population, after median follow-up of 51 months, we observed a significant difference in OS only with the Ki67 cut-off of 30% (67 vs 64 months, p=0.04, HR=0.79 IC à 95% [0.6–0.87]). In node negative pN0 population, Ki67 cut-off=20% was significantly associated with OS (72 vs 65 months, p=0.03, HR=0.83[0.63–0.92]). In node positive tumours different Ki 67 cut-off values did not predict survival except in ≥4pN+ group, where patients with Ki67>50% had significantly worse OS compared to patients≤50% (63 vs 30 months, p=0.01, HR=0.31 IC à 95% [0.22–0.65]).

Conclusions Ki67 level in RH+/HER2- breast cancer predicted survival with the cut-off value of 30%. Ki67 had an impact on survival with a cut-off=20% in node negative and 50% in ≥4pN+ tumours.