Immunohistochemistry assay with EGFR L858R was positive in 19 (86%) of the HER2-positive breast carcinomas and negative in all HER2-negative carcinomas.
Full-section immunohistochemical staining detected heterogeneous mutant EGFR proteins expression in tumours, and revealed L858R mutation in the non-neoplastic bronchial epithelium adjacent to EGFR L858R-carrying carcinomas in three of 16 (19%) cases.