To test for Ki-67,* your doctor may send a sample of previously biopsied breast cancer tissue to a lab for analysis. You'll receive the results in your pathology report, which will show what percentage of cancer cells express Ki-67. In the monarchE study, Ki-67 levels ≥20% indicated 'high' Ki-67. If levels of Ki-67 are high, that means cancer cells are quickly dividing and creating new cells.