Screening-detected breast cancers: discordant independent double reading in a population-based screening program.

PURPOSE: To analyze discordant and concordant screening-detected breast cancers in a nationwide population-based screening program by using independent double reading with consensus.

MATERIALS AND METHODS: The study is a part of the evaluation of the Norwegian Breast Cancer Screening Program and is covered by the Cancer Registry regulation. Analyses were based on prospective initial interpretation scores of 1 033 870 screenings that included 5611 breast cancers. A five-point scale for probability of cancer was used in the initial interpretation. Screening mammograms with a score of 2 or higher by either radiologist were discussed at consensus meetings where the decision whether to recall was made. A score of 1 by one reader and 2 or higher by the other was defined as a discordant interpretation and discordant cancer, whereas a score of 2 or higher by both readers was defined as a concordant recall and cancer.

RESULTS: Discordant interpretation was present in 5.3% (54 447 of 1 033 870) of the screenings, whereas 2.1% (21 928 of 1 033 870) were concordant positive interpretations. Of the screening-detected cancers, 23.6% (1326 of 5611) were diagnosed in women who were recalled because of screenings with discordant interpretation. One hundred seventeen interval breast cancers were diagnosed among the 40 312 screenings that were dismissed at consensus; these were 6.5% of all interval cancers. A significantly higher proportion of microcalcifications alone was present in discordant cancers (24.9% [304 of 1219]) compared with concordant cancers (17.7% [704 of 3972]) (P < .001).

CONCLUSION: Independent double reading with consensus at mammography screening has the potential to increase the cancer detection rate compared with single reading. Mammograms with microcalcifications alone are significantly more common among discordant cancers.