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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.
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.
In plain words · 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.
Ki-67 tells you how fast the cancer is growing. In a neuroendocrine tumour it sets the grade, which steers treatment. In early breast cancer a high Ki-67 (20 percent or more) was once required for adjuvant abemaciclib; it no longer is, but the number still helps your team judge how much benefit chemotherapy or a CDK4/6 inhibitor is likely to add.
Written only from the label or guideline text cited on this page. Not medical advice; your own report and the reading your team gives it come first.
Percentage of tumour cell nuclei staining for Ki-67 (MIB-1), counted in the invasive tumour; in monarchE cohort 2 a score of 20 percent or more was required, measured centrally with the Ki-67 IHC MIB-1 pharmDx.
“Breast tumor samples were tested at central sites using the Ki-67 IHC MIB-1 pharmDx (Dako Omnis) assay to establish if the Ki-67 score was ≥20%.”
Verzenio prescribing information (clinical studies section)No approval uses this readout as a threshold. It is defined by WHO Classification of Tumours, Digestive System Tumours, 5th edition (neuroendocrine grading by Ki-67).
| Threshold | Drug | Cancer | Regulator | Source |
|---|---|---|---|---|
| Ki-67 >= 20% (2021 adjuvant approval, requirement removed March 2023)historic The current label no longer restricts adjuvant abemaciclib by Ki-67; the threshold is kept as the historic 2021 approval condition. | Abemaciclib | High-risk early HR-positive breast cancer | FDA | label |
Matched on the name and aliases of the readout in the title, setting and summary of each trial; a match is a mention, not proof the readout was an entry criterion.
Shares Immunohistochemistry (IHC), HR-positive / HER2-negative breast cancer and the tag biomarker.
Shares Immunohistochemistry (IHC), HR-positive / HER2-negative breast cancer and the tag biomarker.
Shares Immunohistochemistry (IHC), HR-positive / HER2-negative breast cancer and the tag biomarker.
Shares Immunohistochemistry (IHC), HR-positive / HER2-negative breast cancer and the tag biomarker.
Shares Somatostatin receptor expression by PET (SSTR-positive) and the tag biomarker.
Shares Immunohistochemistry (IHC) and the tag biomarker.
Shares Immunohistochemistry (IHC), HR-positive / HER2-negative breast cancer and the tag biomarker.
Shares Immunohistochemistry (IHC) and the tag biomarker.
Every source this page cites, grouped by who published it. Grouping is read from the web address, not assigned by hand.
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