ERBB2 (HER2) P780_Y781insGSP (also referred to as G778_P780dup) results in the insertion of three amino acids in the protein kinase domain of the Erbb2 (Her2) protein between amino acids 780 and 781 (UniProt.org). P780_Y781insGSP results in constitutive activation of Erbb2 (Her2), increased downstream signaling, and is transforming in cell culture (PMID: 23220880, PMID: 28363995, PMID: 29967253).