Ki67--no evidence for its use in node-positive breast cancer.

The expression of Ki67 in breast cancer has been associated with the luminal B phenotype, a high risk of relapse, and likelihood of good response to neoadjuvant chemotherapy. Several guidelines propose assays to determine Ki67 expression levels to select which patients with early stage breast cancer and 1-3 positive axillary nodes should not receive adjuvant chemotherapy. We discuss why oncologists should not rely on the use of this biomarker for patients with early stage breast cancer and only 1-3 positive axillary nodes. First, Ki67 staining lacks analytical validity. Second, the performance of the biomarker for prognostic purposes is poor, with no compelling evidence to indicate that patients with oestrogen receptor (ER)-positive disease, low Ki67 expression and 1-3 positive axillary nodes have a very low risk of disease relapse. Finally, no robust evidence indicates that Ki67 staining predicts the efficacy of adjuvant chemotherapy. Overall, evidence does not support withholding adjuvant chemotherapy in patients with ER-positive, Ki67-low breast cancer and 1-3 positive nodes without risk in daily practice.