Purpose: Patients with mutations of epidermal growth factor receptor (EGFR) receive more benefit from EGFR-tyrosine kinase inhibitor treatment. However, usually such treatment is used to treat advanced lung cancer and only small biopsy samples are available for mutational analysis. We used immunohistochemistry to examine recently developed antibodies specific to major hotspot mutations of L858R and DEL E746-A750.
Experimental design: We used five series of lung cancers: 47 non-small cell lung cancers (NSCLC) to evaluate various types of EGFR mutations, a consecutive series of 238 NSCLCs to study the sensitivity and specificity, 11 NSCLCs with both EGFR mutation and amplification to examine the spatial distribution, 32 patients treated with gefitinib to compare clinical responses, and 15 NSCLCs to explore changes associated with acquired T790M mutation.
Results: Each antibody specifically recognized the corresponding mutation but also recognized other types of mutations. Overall specificity and sensitivity were 96% and 47%, respectively. The positive reaction showed heterogeneous distribution that agreed with the expression of the total EGFR molecule, part of which was associated with gene amplification. A clinical response to gefitinib treatment correlated with the reaction, although one of the two patients with a positive reaction responded well despite having the wild-type EGFR. Acquired T790M mutation did not change the reaction to the antibodies.
Conclusions: On some characteristics, the positive reaction to mutation-specific antibodies differs from the molecular EGFR mutation. Therefore, this study revealed that not all patients with EGFR mutations can be selected using these mutation-specific antibodies.