Ki-67
Pronunciation: KAY-eye-sixty-seven
A protein marker that indicates how quickly cancer cells are dividing, expressed as a percentage of positive-staining cells.
Full Definition
Ki-67 is a nuclear protein associated with cellular proliferation and is used as a biomarker to assess the growth rate of breast cancer cells. The Ki-67 proliferation index is expressed as the percentage of cancer cell nuclei that stain positive for this marker. Higher Ki-67 levels generally indicate more aggressive tumors with faster cell division. In breast cancer, Ki-67 is particularly important in luminal breast cancers to help distinguish between luminal A and luminal B subtypes, with implications for chemotherapy decisions.
Usage
Usage note: Always include percentage when reporting Ki-67 values.
In Context
- "The Ki-67 proliferation index was 25%, suggesting intermediate-grade tumor biology." — Pathology report
- "A Ki-67 of less than 14% supports classification as luminal A subtype." — Molecular subtyping report