From the Guidelines
A low Ki-67 score is typically considered to be less than 5%, as recently endorsed by an international consensus committee. The Ki-67 protein is a cellular marker for proliferation, and the Ki score (or Ki-67 index) measures the percentage of cancer cells that are actively dividing. Scores below 5% generally indicate a slow-growing tumor with lower proliferative activity, which is important for determining treatment strategies and prognosis 1. In breast cancer specifically, the interpretation of Ki-67 scores can vary slightly between different medical institutions, but a score below 5% is often classified as low 1.
Key Points to Consider
- The Ki-67 score is a significant factor in evaluating cancer behavior and planning treatment.
- A low Ki-67 score is associated with a better prognosis and less aggressive tumor behavior.
- The recent international consensus committee endorsed a threshold of 5% for rejecting or recommending adjuvant chemotherapy in ER+ early breast cancer 1.
- Quality assurance programs are essential for laboratories reporting Ki-67 scores to ensure accurate interpretation.
Clinical Implications
- Oncologists use the Ki-67 score, along with other factors, to determine appropriate treatment strategies for patients with breast cancer.
- Patients with low Ki-67 scores may require less intensive treatment approaches, while those with higher scores may require more aggressive treatments.
- The Ki-67 score is an important tool for personalized medicine, allowing clinicians to tailor treatment plans to individual patients' needs.
From the Research
Definition of Low Ki-67 Score
- A low Ki-67 score is generally considered to be less than 10% 2, although different studies have used varying cut-off levels to define low Ki-67 expression.
- For example, one study defined low Ki-67 as less than 14% 3, while another study used a cut-off of 20% to define high Ki-67 expression 4, 5, 3.
- The choice of cut-off level may depend on the specific context and population being studied, as well as the desired level of sensitivity and specificity.
Ki-67 Cut-Off Levels and Prognostic Value
- A study found that a Ki-67 cut-off of 25% was associated with a greater risk of death compared to lower expression rates 4.
- Another study found that a Ki-67 cut-off of 20% was more reliable in differentiating patients at low or high risk of recurrence and death 3.
- The prognostic value of Ki-67 may also depend on other factors, such as progesterone receptor expression 6.
- High Ki-67 expression has been associated with poorer outcomes, including lower disease-free survival and overall survival rates 2, 4, 5, 3, 6.
Clinical Implications
- The definition of a low Ki-67 score and the choice of cut-off level may have implications for clinical decision-making, including the use of adjuvant therapies and the prediction of patient outcomes.
- Further research is needed to determine the optimal Ki-67 cut-off level and to fully understand the prognostic value of Ki-67 in different clinical contexts 2, 4, 5, 3, 6.