Assessing sizes of breast cancers that show non-mass enhancement on MRI based on inter-observer variability and comparison with pathology size

Background Magnetic resonance imaging (MRI) is largely used for preoperative evaluation of breast cancer. Purpose The aim of this study is to evaluate inter-observer variability for measuring the sizes of non-mass enhancement (NME) breast cancers on various sequences of MRI and to compare with pathology size. Material and Methods From January 2013 to April 2017, 70 breast cancers in 70 women showed NME on preoperative MRI. Three observers retrospectively measured the cancers with the longest diameters on subtracted early dynamic contrast-enhanced (DCE) T1 (early T1), delayed DCE T1 (delayed T1), and maximum intensity projection (MIP) images; the measurements between observers were analyzed using the intraclass correlation coefficient (ICC). Pathology sizes were compared using ICCs and Bland-Altman plots, and concordance rates were calculated with MRI and pathology size differences of <= 0.5 cm. Results The ICC for the three observers' breast cancer size measurements was excellent (0.945) and that between MRI and pathology size was good to excellent in all observers (0.742-0.850). Compared with pathology size, the Bland-Altman plots revealed a positive trend of differences in all MRI measurements. Three observers overestimated nearly half of the measured breast cancers on all three MRI sequences; the overestimation rates were the highest on MIP for observers 1 and 3 (68.6% and 55.7%) and on delayed T1 for observer 2 (57.1%). Conclusion The size assessments of NME breast cancer on MRI showed high correlation between observers and with pathology size. However, MRI measurements need a cautious approach because of their high overestimation rates. Measurements from early T1 images showed the highest concordance rate with pathology size.