Retrospectively visible cancers are defined as interval cancers or screen-detected cancers (missed cancers) which are judged visible on prior screening mammogram. There are two kinds of retrospectively visible cancers: "actionable" cancers and nonspecific findings that do not warrant recall in normal practice. Nonspecific findings are twice more frequent than actionable cancers. The rate of missed breast cancers in screening is estimated at 25% (13-41%). Missed breast cancers are masses or calcifications. Masses are twice more frequent than calcifications. Missed breast cancers result from detection errors (location in retroglandular region or at the edge of glandular tissue, architectural distorsion) and interpretation errors (findings judged as benign). Detection errors could be limited by double reading and CAD, interpretation errors by better knowledge of BIRADS classification which needs specific training.