In the KRISTINE trial, which evaluated neoadjuvant T-DM1 and pertuzumab compared to trastuzumab, pertuzumab, docetaxel, and carboplatin, patients experiencing locoregional progression before surgery showed a higher heterogeneity in tumor cell populations, with variable HER2 IHC expression in 80% of the tumor cells. Here, ERBB2 is linked to neoplasm.