Comparison of CISH and FISH for detection of EGFR copy number in lung adenocarcinoma and correlation with EGFR and KRAS mutation status and EGFR immunoreactivity.

22105 Background: EGFR copy number has been shown to correlate with the presence of EGFR mutations and response to tyrosine kinase inhibitors (TKIs) in patients with lung adenocarcinoma. Fluorescent in situ hybridization (FISH) for EGFR has been more widely used than chromogenic in situ hybridization (CISH) but the latter offers some advantages in terms of equipment, ease of implementation and preservation of results. We compared CISH and FISH for EGFR in a series of lung adenocarcinomas and correlated the findings with EGFR and KRAS mutation status and EGFR expression by immunohistochemistry (IHC).,A tissue microarray was constructed containing triplicate cores of 28 EGFR mutated lung adenocarcinomas and 31 EGFR non-mutated cases, the latter including 8 KRAS mutated cases. For both ISH methods, nuclear counts of 5 or more signals were scored as positive. The criteria for FISH include polysomy or high copy number. EGFR IHC was scored from 0-3 with 0 and 1 counted as negative and 2 and 3 as positive.,Overall correlation of CISH and FISH was excellent. 20 of 59 (33%) cases were amplified by CISH and 23 of 59 (37%) were amplified by FISH, with 18 (30%) positive and 34 (57%) negative by both methods (p<0.0001). Discordant cases included 5 negative by CISH and positive by FISH and 2 positive by CISH and negative by FISH. Of 20 EGFR CISH positive cases, 15 (75%) were mutated (p=0.003) and of the 23 FISH positive cases, 16 (70%) were mutated (p=0.007). One case called positive by FISH, negative by CISH showed a KRAS mutation. No other KRAS mutant case was scored as EGFR-amplified by either method. EGFR was positive by IHC in 28 cases, of which 15 were positive by CISH (p=0.003) and 16 by FISH (p=0.007). There was no correlation with IHC and mutations status.,EGFR CISH and FISH show excellent concordance in scoring EGFR amplification, which shows a highly significant association with EGFR mutation. No significant financial relationships to disclose.