MKI67 and breast neoplasm: The immunohistochemical classification of breast tumor samples within the combined AHSB + FIVO cohort into Ki67 + low (< 14%) and Ki67 + high (> 14%) groups showed that RRAS2 expression was significantly higher in the Ki67 + > 14% group, suggesting that higher RRAS2 expression in breast cancer tumors is associated with a worse prognosis (Fig. 6a).