ERBB2 and neoplasm: Regarding anti-HER2 therapy, in a preclinical study, Syed and coworkers found that, in a mouse model with a HER2-positive tumor, both vascular heterogeneity and cellularity heterogeneity increased after trastuzumab treatment, as indicated by increases in the mean K–S distance for the Ktrans distribution and Ve distribution, respectively.293 An increase in cellularity heterogeneity in trastuzumab-treated tumors is expected with increased tumor cell death.