From the Guidelines
The Ki67 labelling index is reported as the percentage of positive tumor cells in the area of highest nuclear labeling. This index is a crucial measure of cell proliferation, primarily used in cancer diagnostics, including neuroendocrine tumors, as noted in a study published in the Journal of the National Comprehensive Cancer Network 1. The Ki67 index represents the proportion of tumor cells that stain positive for the Ki67 protein, which is present in actively dividing cells.
Key Points to Consider
- The index is calculated by counting the proportion of Ki67-positive cells among the total tumor cell population examined under a microscope after immunohistochemical staining.
- Although counting 2000 tumor cells is recommended to determine the Ki-67 index, estimation is currently acceptable in routine clinical practice due to practical limitations, as acknowledged in the study 1.
- The Ki67 index is vital for determining prognosis, guiding treatment decisions, and classifying tumors into molecular subtypes, with higher values indicating more aggressive tumors.
- In cases where both mitotic rate and Ki-67 index are used and yield discordant results, the higher grade is assigned, emphasizing the importance of considering both factors for accurate tumor grading 1.
From the Research
Definition of Ki67 Labelling Index
- The Ki67 labelling index (LI) is a measure of the proportion of staining cells, widely used to reflect proliferation in carcinomas 2.
- It is defined as the percentage of cells that express the Ki67 antigen, which is a marker of cell proliferation 3.
Clinical Significance of Ki67 Labelling Index
- The Ki67 labelling index has prognostic and predictive value in patients with early-stage breast cancer, particularly in hormone receptor-positive, HER2-negative (luminal) tumours 4.
- A high Ki67 labelling index is associated with adverse clinicopathological parameters, such as histopathological grading, clinical TNM staging, and nodal metastasis 5.
- The Ki67 labelling index can predict clinical outcome and survival in oral squamous cell carcinoma, with higher indices associated with poorer survival rates 5.
Measurement and Interpretation of Ki67 Labelling Index
- The Ki67 labelling index can be measured using immunohistochemistry on tissue samples 2, 5.
- The index is calculated as the percentage of positively stained cancer cells, with different cut-off values used to distinguish between tumours with low and high proliferative activity 2, 6.
- The choice of cut-off value is important, with some studies suggesting that values ending with 0 or 5 may be more realistic 2.
Ki67 Labelling Index in Cancer Therapy
- Ki67 is a promising target for cancer therapy, with its high expression in malignant cells and low expression in normal cells making it an attractive target for targeted therapies 3.
- The Ki67 promoter can be used to drive the expression of therapeutic genes or siRNAs in cancer cells, providing a new avenue for cancer therapy 3.