Here, we presented a heavy pretreated and harbored HER2 V777L mutation de novo stage IV Luminal B (HER2 unamplified) breast cancer patient who achieved an unexpected good response to trastuzumab combined with vinorelbine therapy.
This was identified in one of six cases of a HER2-amplified breast cancer, both pre- and post-treatment; however, HER2 V777L was not identified in 14 responders who were treated with trastuzumab.
In an independent data set, 2 of 9 (22.2%) ERBB2/HER2-negative BrCa switched to ERBB2/HER2-positive with 1 BrM acquiring ERBB2/HER2 amplification and the other showing metastatic enrichment of the activating V777L ERBB2/HER2 mutation.