ERBB2 and neoplasm: Although surprising, this finding is supported by three observations of ours: (a) HER2 levels were high and/or increased in 4/5 tested post-T-DM1 tumor re-biopsies, and all these were aHER2-neutral (Fig. 3); (b) although assessed in two patients only, aHER2 and sHER2 kinetics were reciprocal (Fig. 2d); (c) HER2 split was not seen at progression from Trastuzumab and was rare at progression from double Trastuzumab/Pertuzumab blockade (Fig. S2).