Ki-67 is a nuclear, non-histone protein that is expressed only
during active phases of the cell cycle (G1, S, G2 and M), but
not in the resting phases (G0 and G1 early phase). Although
the antigen has also been associated with ribosomal RNA
transcription, it is strongly linked to cell proliferation and has
thus been indicated as an e‑ective marker in grading the
proliferation rate of tumors, including those of the brain,
breast, cervix, and prostate
