Of the 427 cancers detected by screening (5.5 per 1,000 women screened), 321 (75.2%) were detected by both the field radiologist and the expert, 62 (14.5%) by the expert only and 44 (10.3%) by the field radiologist only. The overall rate of agreement between the two readers was 97.8% and agreement was better for cancerous than for non-cancerous lesions. The majority of false-positives (54%) were recalled by the field radiologist alone, 19% were recalled by the expert alone and 26% by both readers. A system with single reading by a non-expert would recall 3.7% of women, would miss at least 62 cancers and would increase specificity by 0.7% with respect to the dual reading system. A system with expert reading only would recall 2.3% of women, would miss at least 44 cancers and cause 9.4% fewer benign biopsies and increase specificity by 2.1%.