de Paz Villanueva CC, et al. - The factors associated with underestimating invasive cancer in patients with a clinical diagnosis of non–high-grade ductal carcinoma in situ (DCIS) that preclude active surveillance were determined. It was suggested considering factors other than tumor biology associated with invasive carcinoma based on final pathologic findings when selecting patients for active surveillance of DCIS. A significant proportion of patients with non–high-grade DCIS will harbor invasive carcinoma at the time of randomization to active surveillance.