Detection of epidermal growth factor receptor mutations in non-small cell lung cancer by immunohistochemistry.

Objectives To evaluate the sensitivity and specificity of immunohistochemistry (IHC) for detecting common epidermal growth factor receptor (EGFR) mutations in non-small cell lung cancer (NSCLC) and to estimate the cost-effectiveness of IHC testing. Methods A total of 208 NSCLC patients were included in the trial, and the EGFR mutation status in the patients were detected by PCR and IHC. Two mutation-specific antibodies against the most common exon 19 deletion (clone SP111) and exon 21 L858R mutation (clone SP125) were tested by using automated immunostainer. A cost-effectiveness analysis model was built for the analysis of optimal detection scheme. Results With a cutoff value of IHC 1+, the overall sensitivity and specificity of the IHC-based method compared with the PCR-based method were 81.7% (95% CI 72.4% to 89.0%) and 94.7% (95% CI 92.6% to 99.5%), respectively. EGFR 19del mutation was detected by SP111 antibody with a sensitivity of 65.9% (95% CI 49.4% to 79.9%) and specificity of 98.8% (95% CI 95.7% to 99.9%). EGFR L858R mutation was detected by SP125 antibody with a sensitivity of 94.2% (95% CI 84.1% to 98.8%) and specificity of 99.4% (95% CI 96.5% to 100%). The IHC and PCR cost ratio needed to be 1-to-3 or more in our patients to economically justify before the use of IHC. Conclusions The study confirms an excellent specificity with fairly good sensitivity of IHC and mutation-specific antibodies for common EGFR mutations. It is cost-effective to use IHC method to detect EGFR mutation first when the IHC and PCR cost ratio is 1-to-3 or more in Chinese populations.