# Ki-67 (MKI67)

Source: https://onco.cc/targets/mki67/  
OnCo record `mki67` (Target). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Ki-67 is a protein present only in cells that are dividing, so the share of tumour cells that stain for it is a direct read of how fast the cancer is growing.

## Summary

MKI67 encodes a large nuclear protein expressed through the active phases of the cell cycle and absent in resting (G0) cells. The Ki-67 labelling index by immunohistochemistry (antibody MIB-1 on paraffin sections) grades neuroendocrine tumours in the WHO classification and is read in breast cancer as a proliferation marker; the abemaciclib adjuvant approval of 2021 used a Ki-67 score of at least 20 percent as an entry criterion before the label was broadened in 2023. It is a readout, not a drug target: no approved medicine binds Ki-67.

## Fields

- Kind: Target
- Last checked: 2026-09-23
- Also known as: Ki67; MIB-1; marker of proliferation Ki-67
- Tags: biomarker-parent
- Symbol: MKI67
- Class: other
- Biology: Ki-67 coats the surface of mitotic chromosomes and keeps them from clumping; its level rises through S, G2 and M phase and falls to nothing in quiescent cells, which is why the stained fraction tracks proliferation.
- Where found: Breast cancer (proliferation index); Neuroendocrine tumours (WHO grade); Lymphomas and gliomas (proliferation index)

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Ki-67_(protein)
- HGNC HGNC:7107: https://www.genenames.org/data/gene-symbol-report/#!/hgnc_id/HGNC:7107
- UniProt P46013: https://www.uniprot.org/uniprotkb/P46013/entry

## Connected records

- biomarkers: [Ki-67 index (proliferation by IHC)](https://onco.cc/biomarkers/ki-67-index/)
- cancers: [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [Neuroendocrine tumours](https://onco.cc/cancers/neuroendocrine/)
- terms: [Immunohistochemistry (IHC)](https://onco.cc/terms/ihc/), [Neuroendocrine tumour grade (Ki-67) and WHO classification](https://onco.cc/terms/net-grade-ki67/), [Proliferation](https://onco.cc/terms/proliferation/)
- collections: [CIViC](https://onco.cc/collections/civic/)

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JSON: https://onco.cc/api/v1/entities/mki67.json