The Proper Ki-67 Cut-Off in Hormone Responsive Breast Cancer: A Monoinstitutional Analysis with Long-Term Follow-Up.

Introduction: Breast cancer is a heterogeneous disease. Our study focuses on a monoinstitutional series of patients affected by Hormone Responsive carcinomas (luminal A and luminal B) and aims to define an optimal Ki-67 cut-off, to correctly stratify these patients into risk classes, using the ImmunoHistoChemical (IHC) surrogates of the Molecular Subtypes, according to the St. Gallen guidelines.

Methods: We analyzed 1685 patients. These patients underwent both radical and conservative surgeries with Sentinel Lymph Node Biopsy eventually followed by Axillary Dissection (AD). Furthermore, all the patients underwent adjuvant therapies according to the guidelines. A retrospective univariate analysis was performed and survival curves (Disease-Related Survival, DRS, and Disease-Free Survival, DFS) were carried out according to the following ki-67 risk classes: Low Risk (Ki-67 ≤ 14%); Intermediate Risk (Ki-67 15% ÷ 20%); High Risk (Ki-67 > 20%).

Results: 14 yy DRS was 98% in LA and 85% in LB with a ki-67 cut-off of 14% (p=0.037) vs 95% (LA) and 83% (LB) with a ki-67 cut-off of 20% (p=0.003). 14yy DFS was 85% in LA and 72% in LB with a ki-67 cut-off of 14% (p=0.017) vs 83% (LA) and 66% (LB) with a ki-67 cut-off of 20% (p<0.000).

Discussion: Our results confirmed that the 20% Ki-67 cut-off is more reliable in differentiating patients at low or high risk of recurrence and death, and stratifying patients eligible for adjuvant chemotherapy. Thus, despite its poor reproducibility, the identification of the most accurate ki-67 index assumes a pivotal relevance in guiding a tailored strategy among patients with this specific profile of breast cancer, as well as the molecular surrogates, in order to avoid harmful overtreatments.