Magnetic resonance imaging and ultrasound for prediction of residual tumor size in early breast cancer within the ADAPT subtrials

Abstract Background: Prediction of histological tumor size by post-neoadjuvant therapy (NAT) ultrasound and magnetic resonance imaging (MRI) was evaluated in different breast cancer subtypes.Methods: Imaging was performed after 12-week NAT in patients enrolled into three neoadjuvant WSG ADAPT subtrials. Imaging performance for prediction of tumor size was analyzed across increasing size ranges (≤10, ≤20 and ≤30 mm) and summarized using positive (PPV) and negative predictive values (NPV).Results: 248 and 588 patients had MRI and ultrasound, respectively. Tumor size was over- or underestimated by <10 mm in 4.4% and 21.8% of patients by MRI and in 10.2% and 15.8% by ultrasound. Overall, PPV (correctly predicted tumor size ≤10, ≤20 or ≤30 mm) of MRI and ultrasound increased from 0.61 and 0.72 for ≤10 mm tumors to 0.88 and 0.96 for ≤30 mm tumors; NPV (correctly predicted tumor size >10, >20 or >30 mm) decreased from 0.89 and 0.74 to 0.69 and 0.22. Across all tumor size ranges, ultrasound demonstrated higher PPV than MRI in HR+/HER2+ tumors while both methods had a similarly low PPV in HR-/HER2- and HR-/HER2+ tumors. MRI had a higher NPV than ultrasound with the exception of HR-/HER2- tumors measuring ≤10 and ≤20 mm where both methods had similar NPV. Conclusions: Ultrasound is less likely than MRI to underestimate the size of HR+/HER2+ tumors while MRI is associated with a lower risk to overestimate the size of HR+/HER2+ and HR-/HER2+ tumors. These findings may help to select the most optimal imaging approach for planning surgery after NAT. Trial registration: Clinicaltrials.gov, NCT01815242 (registration March 21, 2013, NCT01817452 (registration March 25, 2013), NCT01779206 (registration January 30, 2013).