Abstract: To provide a novel method for determining the risk of lymph node metastasis of breast cancer uses as an index the difference in the expression levels of marker genes in at least one material selected from the group consisting of a breast tissue and a breast cell of a patient. The method includes measuring an expression level of a marker gene in at least one material selected from the group consisting of a breast tissue and a breast cell of a patient with breast cancer, and determining the risk of lymph node metastasis of breast cancer in the patient using the expression level of the marker gene as an index.

Abstract: To provide a novel method for determining the risk of lymph node metastasis of breast cancer uses as an index the difference in the expression levels of marker genes between metastatic breast cancer tissue (or cell) and non-metastatic breast cancer tissue (or cell). The method involves (1) measuring the expression level of a gene having a base sequence in human metastatic breast cancer tissue (or cell), (2) measuring the expression level of the same gene in human non-metastatic breast cancer tissue (or cell), and (3) comparing the expression level of (1) with the expression level of (2) and determine the risk of lymph node metastasis of breast cancer based on the difference between the expression levels.