In our previous study, we found that higher expression of five proliferation-related genes (UBE2C, TOP2A, RRM2, FOXM1, and MKI67) was associated with shorter DMFS in patients with LN−, HR+/HER2− breast cancer, whereas expression of the immune response-related BTN3A2 gene was positively correlated with longer DMFS. The gene discussed is RRM2; the disease is breast cancer.