MKI67 and neoplasm: In contrast to conventional methods of microscopic assessment of nuclear atypia and mitotic figure counting, the 21‐gene assay captures tumor proliferative activity by the quantitation of 5 proliferation genes that include MKI67, the gene for Ki67, and constitute the “proliferation gene axis.”16 The five proliferation genes are assessed as continuous covariates, and their expression average is integrated into the RS result when the group result is at or above the threshold of 6.5 Ct.