A Ki-67 score of 40% or higher in breast cancer is considered high and is associated with a greater risk of death and recurrence. Ki-67 is a protein that's only found in cells that are dividing, and a high score indicates that many cells are dividing quickly. This suggests that the cancer is likely to spread and grow.
According to a 2023 study, the 5-year disease-free survival rate for patients with Ki-67 scores of more than 40% is 72%. For comparison, the rate is 96% for patients with scores of 0–9%, 90% for scores of 10–19%, 80% for scores of 20–29%, and 75% for scores of 30–39%.
