ERBB2 and neoplasm: Despite the mAb104-epitope not being detected in low HER2 expressing cell lines by FACS, we postulate that mAb104 selectively interacts with distinct sub-populations and conformations of HER2 depending on the intra-tumoural conditions in the tumour, as we have demonstrated with an antibody to a similar conformationally exposed epitope of EGFR in animal models and in patients [30].