In order to investigate whether the observed HER2 overexpression or amplification after progression on EGFR TKI treatment was induced by EGFR TKI treatment or if this was already present in the tumour sample prior to EGFR TKI treatment, the pre-EGFR TKI biopsy samples, where available, were analysed for HER2 expression with IHC. The gene discussed is ERBB2; the disease is neoplasm.