ERBB2 and neoplasm: Since intratumoral heterogeneity of HER2 protein expression and gene amplification has been recognized and is inevitable, repeat testing on a subsequent specimen should be considered, particularly if the tumor has histologic characteristics associated with HER2 positivity (i.e., a tumor grade of 2 or 3, a weak or negative PgR expression or an increased proliferation index) [6], or the clinical course is not as expected.