How do you interpret efficacy of trastuzumab deruxtecan based on HER2 mutation type and/or level of HER2 overexpression?  

In the phase 2 DESTINY-Lung01 study, the majority of the HER2 mutation was at exon 20 and were insertion mutations. There were other rare HER2 alterations such as exon 19 and extracellular domain mutation in exon 8 that also responded to trastuzumab deruxtecan. Some of these patients had their HER2 ...

The results with HER2 mutations are more reliable than the protein expression. I perform HER2 testing with my NGS at diagnosis because we did have some trials.