Triple-negative and HER2-positive breast cancers found by mammography screening show excellent prognosis

Our purpose was to explore the prognosis of aggressive breast cancers of the HER2 oncogene amplification (HER2 +) and triple-negative (TN) subtypes detected by screening, as well as the prognosis of interval cancers (clinically due to symptoms between screening rounds) and cancers in screening nonparticipants.

The study population comprised of 823 breast cancers in women aged 50-69 years from 2006-2014. Of these, 572 were found by screening mammography (69%), 170 were diagnosed between the screening rounds (21%), and 81 were diagnosed in women who did not participate in the screening program (10%).

The majority of all HER2 + (59%) and TN cancers (57%) in this age group were detected by screening. Screen-detected HER2 + tumors were small (median 12 mm), and node-negative (84%). During a median follow-up of eight years, the distant disease-free survival of screen-detected HER2 + and TN cancers was better than that of interval and nonparticipant cancers (age-adjusted HR = 0.16, 95% CI 0.03-0.81 and HR = 0.09, 95% CI 0.01-0.79, respectively). In nonparticipants, the distant disease-free survival of these cancers was worse than in participants (age-adjusted HR = 2.52, 95% CI 0.63-10.11 and HR = 5.30, 95% 1.16-24.29, respectively).

In the 50-69 age group, the majority of HER2 + and TN cancers can be found by a quality assured population-based mammography screening. Despite their generally aggressive behavior, after a median follow-up of 8 years, distant disease-free survival was over 90% of these cancers detected by screening. The worst prognosis of these cancers was in women who did not participate in screening.