Índice Ki-67 %
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
About this calculator
The Ki-67 Index is an oncology metric used to assess cell division rates in tumor tissues. It calculates the proportion of active (positive) cells relative to the total cells analyzed, expressed as a percentage (e.g., positive cells/total × 100). This index helps oncologists classify the aggressiveness of certain cancers, such as breast cancer and lymphomas, and plan more precise treatments.
The basic formula is: (number of Ki-67 positive cells ÷ total cells counted) × 100. For example, if 50 out of 200 analyzed cells are positive, the index is 25%. Values above 20% indicate more aggressive tumors, while lower values suggest slower growth. Interpretation varies by cancer type and clinical context.
This tool is useful for oncologists and pathologists during biopsy analysis. It also helps patients better understand their lab results. However, it's crucial to remember that the Ki-67 Index is just one diagnostic parameter. It should be combined with other tests, such as hormonal or genetic markers, for a comprehensive evaluation.
Important precautions: calculation accuracy depends on sample quality and counting techniques. Anomalous results may arise from factors like tumor heterogeneity or human error. Always consult a specialized physician to interpret the Ki-67 Index in a clinical context, avoiding isolated conclusions based solely on this data.
Frequently asked questions
What is the Ki-67 Index?
It is a biological marker that measures cell division activity in tumor tissues. High values indicate accelerated cell growth, associated with more aggressive tumors.
How does the index affect treatment choice?
In some cancers, like breast cancer, tumors with high Ki-67 may require more intensive therapies. The index helps determine if a patient will respond well to chemotherapy or immunotherapy.
What's the threshold between high and low index?
There's no universal cutoff, but values above 20% are generally considered high. Interpretation depends on cancer type and other markers.
Why do results vary?
Variability occurs due to sample differences, analysis techniques, or even tumor heterogeneity. Confirm with complementary tests for accuracy.
Can the Ki-67 Index change over time?
Yes, the index may change as the tumor progresses or after treatments. Periodic tests are required to monitor changes.