HER1-4 expression status correlates with the efficacy of gefitinib treatment and tumor cell proliferative activity in non-small cell lung cancer

The expression of human epidermal growth factor receptor (HER) family proteins was examined in specimens of 52 non-small cell lung cancers to evaluate their significance in tumor cell proliferation and their response to gefitinib. Epidermal growth factor receptor (EGFR; HER1) protein was expressed most frequently (43/52 cases). HER2 and HER3 were detected in 13 and 18 cases, respectively. HER4 was detected in only one case of squamous cell carcinoma. HER3 was expressed preferentially in adenocarcinomas of the papil- lary type. In most HER3-positive cases with or without other HER family proteins, the Ki-67 labelling index (18.2%) was significantly lower than in HER3-negative cases (30.6%) (P