The accuracy of MRI in detecting pathological complete response following neoadjuvant chemotherapy in different breast cancer subtypes

Pathological complete response (pCR) following neo-adjuvant chemotherapy (NACT) for breast cancer is associated with improved disease-free and overall survival in certain breast cancer subtypes. Magnetic Resonance Imaging (MRI) is increasingly used as standard to assess treatment response in patients receiving NACT. The aim of this study was to determine the clinical utility of MRI in accurately predicting pCR post-NACT. A single-centre, retrospective study was conducted in breast cancer patients, who received NACT between 2013 and 2020. Patients who had an MRI before and after NACT were included. Pathological and MRI radiological response rates to NACT were analyzed and MRI accuracy assessed in detecting pCR according to breast cancer subtype. One hundred and sixty-seven patients were included in the study. Forty-one of the 167 patients achieved pCR (24.6 %), with the highest proportion in HR- HER2+ subgroup (58.3 %), followed by triple negative breast cancer (TNBC) (35 %). Only 22.2 % and 10.5 % of patients with HR + HER2+ and HR + HER2-respectively achieved pCR. The overall accuracy of MRI in predicting pCR after NACT was 77.3 %. The greatest accuracy was in TNBC (87.5 %) with a specificity and positive predictive value (PPV) of 100 % and the highest number of correctly diagnosed complete responses (14 of 40). MRI was less accurate in predicting response rates in HR + HER2- (PPV 91.2 %) and HR + HER2+ groups (PPV 90.5 %). MRI performed significantly better in predicting complete response in TNBC compared to HR + HER2-subtype (p = 0.0057). MRI is a clinically useful adjunct in assessing pCR following NACT and appears to predict pathological response more accurately in TNBC compared to HR + HER2-breast cancer subtypes. This has significant clinical implications in terms of surgical planning, adjuvant treatment options and prognosis.