To study the effect of supplemental MRI on the incidence of interval breast cancers in breast cancer screening participants with extremely dense breast tissue.
Multicenter, randomized, controlled trial (ClinicalTrials.Gov number NCT01315015).
Between 2011-2015 breast cancer screening participants (aged 50-75) with extremely dense breast tissue and normal results on screening mammography were randomized to a group that was invited to undergo supplemental MRI or to a group that received mammography screening only. The primary outcome was the between-group difference in the incidence of interval cancers during the first 2-year screening interval. Secondary outcomes included supplemental cancer detection with MRI and positive predictive values (PPV) for referral and biopsy.
We assigned 40,373 women to an invitation for supplemental MRI screening (n = 8061) or to mammography screening only (n = 32,312). The interval-cancer rate was 5.0 per 1000 screenings in the mammography-only group, and 2.5 per 1000 screenings in the MRI-invitation group, for a difference of 2.5 per 1000 screenings (95% confidence interval [CI]: 1.0-3.7; p<0.001). Of the women who were invited to undergo MRI, 59% accepted the invitation. Of the 20 interval cancers that were diagnosed in the MRI-invitation group, 4 were diagnosed in the women who actually underwent MRI (0.8 per 1000 screenings) and 16 in those who did not accept the invitation (4.9 per1000 screenings). Of the women who underwent MRI, 454 were referred and 79 were diagnosed with breast cancer (PPV 17.4%; 95%-CI:14.2-21.2). The PPV for biopsy was 26.3% (95%-CI:21.7-31.6). The cancer detection rate among women who underwent MRI was 16.5 per 1000 screenings (95%-CI:13.3-20.5).
Supplemental MRI screening in women with extremely dense breast tissue results in fewer interval cancers than screening with mammography alone.
Conflict of interest and financial support: potential conflicts of interest have been reported for this article. ICMJE forms provided by the authors are available online along with the full text of this article.