1. ¹Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
2. ²Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
3. ³Department of Chest Surgery, Kaohsiung Veteran General Hospital, Kaohsiung, Taiwan
4. ⁴Department of Family Medicine, Graduate Institute of Occupational Safety and Health, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan
5. ⁵Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA
6. ⁶Pulmonary and Critical Care Unit, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA

Correspondence: Dr LR Chirieac, MD, Department of Pathology, Brigham and Women's Hospital, 75 Francis Street, Boston, MA 02115, USA. E-mail: lchirieac@partners.org

Received 21 April 2007; Revised 30 June 2007; Accepted 3 July 2007; Published online 3 August 2007.

Abstract

Epidermal growth factor receptor (EGFR) gene copy number correlates with response to tyrosine kinase inhibitors in patients with nonsmall cell lung carcinoma. Fluorescence in situ hybridization (FISH), a standard methodology to detect EGFR copy number abnormalities in nonsmall cell lung carcinoma, is limited by instrumentation and cost. Chromogenic in situ hybridization (CISH) is an emerging alternative detection technique using light microscopy, but its utility in assessing EGFR copy number in lung cancer is not established. To address the utility of CISH, we studied paraffin-embedded nonsmall cell lung carcinoma specimens from 77 Taiwanese nonsmoking women treated by surgery alone. We recorded the number of signals per tumor cell nucleus, correlated EGFR copy number by CISH with FISH results, and used receiver operating characteristics to identify cut-off points for the CISH results. Tumors were classified as adenocarcinoma (n=28), mixed adenocarcinoma with bronchioloalveolar features (n=25), bronchioloalveolar carcinoma (n=2), squamous cell carcinoma (n=15), and adenosquamous carcinoma (n=7). By FISH, 29% of cases had no amplification, 18% had low polysomy, 35% had high polysomy, and 12% had gene amplification. EGFR copy number detected by CISH highly correlated with FISH (Spearman r=0.81, P<0.0001). We determined the optimal EGFR CISH cut-off points that discriminate between no amplification and low polysomy (2.8 signals, P=0.09); no amplification plus low polysomy and high polysomy plus gene amplification (4.5 signals, P<0.0001); and high polysomy and gene amplification (7.1 signals, P=0.0003). CISH is an alternative assay to FISH in determining EGFR copy number status that may contribute to stratification of patients with nonsmall cell lung carcinoma for clinical trials and identify a subset of patients that should be treated with tyrosine kinase inhibitors.