# Ki-67 index (proliferation by IHC)

Source: https://onco.cc/biomarkers/ki-67-index/  
OnCo record `ki-67-index` (Biomarker). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Ki-67 is the percentage of tumour cells that are dividing. In neuroendocrine tumours it sets the grade; in breast cancer a 20 percent cut-off was briefly a condition of adjuvant abemaciclib, then dropped from the label in 2023.

## Summary

The Ki-67 labelling index is the percentage of tumour cell nuclei staining with the MIB-1 antibody. In gastroenteropancreatic neuroendocrine tumours the WHO classification grades G1 (< 3 percent), G2 (3 to 20 percent) and G3 (> 20 percent). In breast cancer the October 2021 FDA approval of adjuvant abemaciclib (monarchE cohort 1) required node-positive, high-risk, HR-positive HER2-negative disease with Ki-67 >= 20 percent by the Ki-67 IHC MIB-1 pharmDx (Dako Omnis) companion diagnostic; the March 2023 label expansion removed the Ki-67 requirement, and the current label describes the assay only in the trial narrative. The International Ki-67 in Breast Cancer Working Group considers scores of 5 percent or less and 30 percent or more reproducible and the range between them not.

## Fields

- Kind: Biomarker
- Last checked: 2026-09-23
- Also known as: Ki-67; Ki67; Ki-67 index; Ki-67 labelling index; Ki-67 score; MIB-1 index; Ki-67 >= 20%; Ki-67 ≥20%; proliferation index
- Tags: biomarker; proliferation

## Sources

- Verzenio prescribing information (DailyMed): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=be4bc0de-0fdc-4d46-8d25-be43c79e6a06

## Connected records

- biomarkers: [ER status (oestrogen receptor by IHC)](https://onco.cc/biomarkers/er-status/), [PR status (progesterone receptor by IHC)](https://onco.cc/biomarkers/pr-status/), [Somatostatin receptor expression by PET (SSTR-positive)](https://onco.cc/biomarkers/sstr-pet-expression/)
- cancers: [High-risk early HR-positive breast cancer](https://onco.cc/cancers/hr-positive-early-high-risk/), [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [Lung neuroendocrine tumours (typical and atypical carcinoid)](https://onco.cc/cancers/lung-net/), [Neuroendocrine tumours](https://onco.cc/cancers/neuroendocrine/), [Pancreatic neuroendocrine tumours](https://onco.cc/cancers/pancreatic-net/)
- drugs: [Abemaciclib](https://onco.cc/drugs/abemaciclib/)
- 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/)
- targets: [Ki-67 (MKI67)](https://onco.cc/targets/mki67/)

---
JSON: https://onco.cc/api/v1/entities/ki-67-index.json