Development of a prediction model for lymph node metastasis in luminal A subtype breast cancer: The possibility to omit sentinel lymph node biopsy

•Genomic nodal index (GNI) was constructed using gene expression microarray.•GNI could predict axillary lymph node metastasis in luminal A breast cancer.•GNI could also predict prognosis of luminal A breast cancer.

The present study aimed to construct a prediction model for axillary lymph node metastasis (ALNM) using a DNA microarray assay for gene expression in breast tumor tissues. Luminal A breast cancers, diagnosed by PAM50 testing, were analyzed, and a prediction model (genomic nodal index (GNI)) consisting of 292 probe sets for ALNM was constructed in a training set of patients (n = 388), and was validated in the first (n = 59) and the second (n = 103) validation sets. AUCs of ROC were 0.820, 0.717, and 0.749 in the training, first, and second validation sets, respectively. GNI was most significantly associated with ALNM, independently of the other conventional clinicopathological parameters in all cohorts. It is suggested that GNI can be used to identify the patients with a low risk for ALNM so that sentinel lymph node biopsy can be spared safely.