Identification of non-small-cell lung cancer with activating EGFR mutations in malignant effusion and cerebrospinal fluid: rapid and sensitive detection of exon 19 deletion E746-A750 and exon 21 L858R mutation by immunocytochemistry.

BACKGROUND: Recently, we have reported that EGFR mutation-specific antibodies performed well in immunohistochemical analysis, with good sensitivity. We investigated whether this method could detect non-small-cell lung cancer (NSCLC) carrying EGFR mutations in malignant effusions and cerebrospinal fluid (CSF), comparable to the peptide nucleic acid-locked nucleic acid (PNA-LNA) PCR clamp assay. Furthermore, we compared activating EGFR mutations between primary and recurrent NSCLC. PATIENTS AND METHODS: Twenty-four patients with NSCLC effusions and CSF were examined by immunocytochemistry using antibodies specific for the E746-A750 deletion mutation in exon 19 and the L858R point mutation in exon 21. The PNA-LNA PCR clamp assay was used to detect the E746-A750 deletion at exon 19, L858R mutation at exon 21, and T790M mutation at exon 20.
RESULTS: We were able to identify EGFR mutations in NSCLC effusion and CSF with a sensitivity of 100% (5/5) using the anti-delE746-A750 antibody and 100% (8/8) using the anti-L858R antibody. Furthermore, in samples without these EGFR mutations, immunocytochemistry with the two specific antibodies identified 91% (10/11) as negative for both the deletion and the point mutations in EGFR. Activating EGFR mutations decreased in recurrent NSCLC compared with primary NSCLC, and the T790M mutation was detected in recurrent NSCLC of patients receiving gefitinib treatment.
CONCLUSIONS: Identification of EGFR mutations is important for patients with primary and recurrent NSCLC. Rapid and sensitive immunocytochemistry using mutation-specific antibodies to detect EGFR mutations will be useful for diagnosing responsiveness to EGFR-targeted drugs.