MKI67 and breast cancer: Given that the mean Ki67 suppression by each of the patient groups in IMPACT was only slightly more at 12 than at 2 weeks, and that 2 weeks is a common duration for the period between breast cancer diagnosis and surgery, the measurement of this biomarker change within what has become known as the presurgical “window of opportunity” has become a primary endpoint in presurgical studies of novel agents.