Initial MRI findings predictive of a pathological complete response to neoadjuvant treatments in HER2-positive breast cancers

•In our study, the presence of a pretherapeutic associated suspicious NME at MRI was predictive of pCR after NST.•This finding was confirmed in a second cohort treated during the same period.•The interobserver reproducibility of the assessment for the presence or absence of an additional suspicious NME at MRI was in good agreement. This study aimed to determine if initial MRI findings could predict a pathological complete response (pCR) following neoadjuvant systemic therapy (NST) in HER2-positive breast cancers. The study retrospectively included 111 patients (Center 1, training set) and 71 patients (Center 2, validation set) with HER2-positive cancer who underwent NST. Initial clinicopathological data and MRI findings were recorded. Continuous variables were analyzed using the Mann–Whitney and Student’s t-tests, while categorical variables were analyzed using the χ2 or Fisher’s exact test. Univariate analysis was conducted to determine the associations between these variables and pathological complete response (pCR), defined as the absence of invasive malignant cells in the breast and lymph nodes. Interobserver reproducibility was assessed for associated non-mass enhancement (NME) parameter by analyzing 50 MR studies (intraclass correlation coefficient). pCR was achieved in 67 patients, 51 (46 %) from Center 1 and 16 (23%) from Center 2 (p = 0.003), with significant differences between Centers 1 and 2 in tumor-infiltrating lymphocyte levels and lymphovascular invasion (p