Understanding / Info
Ki-67
An index that measures the rate at which tumor cells multiply. It is expressed as a percentage — the higher it is, the faster the tumor grows.
What it means
A protein present in cells that are actively multiplying. The Ki-67 value, expressed as a percentage, shows how fast the tumor cells are dividing. A high value indicates a more aggressive tumor.
In short
An index that measures the rate at which tumor cells multiply. It is expressed as a percentage — the higher it is, the faster the tumor grows.
Where you will see it
Mentioned in the immunohistochemistry (IHC) report. Guide values: under 15% = low proliferation; 15–30% = moderate; over 30% = high.
What it does not tell you on its own
Ki-67 on its own does not establish whether the cancer responds to chemotherapy and does not decide the treatment. It is interpreted in context with the type of cancer, the grade and other markers.
Questions for your doctor
- Was Ki-67 measured in my case?
- Does my value mean fast or slow proliferation?
- Does it influence the decision about chemotherapy?
- Should it be correlated with HER2, ER or PR?
Related terms
The terms below often appear alongside this one. Each definition is right here, so you do not have to look elsewhere.
- Immunohistochemistry
- A laboratory technique that uses antibodies to detect specific proteins in tumor cells. It helps establish the exact type of cancer and choose the right treatment, especially in breast, colon and lung cancers.
- HER2
- A protein that can be present in large amounts on the surface of some cancer cells. HER2 positive means that the tumor may respond to specific biological treatments that target this protein.
- Tumor grade (G1–G4)
- A histological classification that shows how different the cancer cell is from the normal cell it came from. G1 means cells that are almost normal (less aggressive), while G4 means cells that are very different (very aggressive). It helps assess how fast the tumor is growing.
Other terms in “Diagnosis”
Glossary definitions are written for patients by the OncoDots team and go through internal medical review. They explain terms; they do not establish a diagnosis and do not recommend a treatment.