Isharwal S, et al. - ERBB2 amplification and HER2 (human epidermal growth factor receptor-2) expression in micropapillary urothelial carcinoma (MPUC) cases were assessed by fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC). Researchers observed the presence of intratumoral heterogeneity of ERBB2 amplification and HER2 expression in MPUC. In the micropapillary (MP) component vs the not otherwise specified (NOS) component within the same tumor, ERBB2 amplification and HER2 overexpression were preferentially but not exclusively detected. ERBB2 amplification was very commonly seen in micropapillary bladder cancer.