 A cluster randomized controlled trial was performed in Bogotá, Colombia between 2007-2008 to evaluate the effects of an opportunistic hospital-based screening program intervention vs. usual care control in which 26 clinics were randomized to an intervention N13 or control arm N13. At intervention clinics general practitioners were instructed to perform clinical breast examination CBE on all women aged 50-69 years attending clinics for non-breast health related issues, and to refer them for mammographic screening. Physicians from control clinics were not specifically instructed to perform breast-screening or refer women for mammography, but could do so if they thought it appropriate usual care. Women were followed for 2 years post-randomization. 