An Na Seo1, Tae-In Park2, Yan Jin3, Ping-Li Sun3, Hyojin Kim3, Hyun Chang4, Jin-Haeng Chung5. 1. Department of Pathology, Seoul National University Bundang Hospital, 300 Gumi-dong, Bundang-gu, Seongnam-si, Gyeonggi 463-707, Republic of Korea; Department of Pathology, Kyungpook National University College of Medicine, 680 Gukchaebosang-ro, Jung-gu, Daegu 700-842, Republic of Korea. 2. Department of Pathology, Kyungpook National University College of Medicine, 680 Gukchaebosang-ro, Jung-gu, Daegu 700-842, Republic of Korea. 3. Department of Pathology, Seoul National University Bundang Hospital, 300 Gumi-dong, Bundang-gu, Seongnam-si, Gyeonggi 463-707, Republic of Korea; Department of Pathology, Seoul National University College of Medicine, 103 Daehak-ro, Jongno-gu, Seoul 110-799, Republic of Korea. 4. Department of Internal Medicine, Seoul National University Bundang Hospital, 300 Gumi-dong, Bundang-gu, Seongnam-si, Gyeonggi 463-707, Republic of Korea. 5. Department of Pathology, Seoul National University Bundang Hospital, 300 Gumi-dong, Bundang-gu, Seongnam-si, Gyeonggi 463-707, Republic of Korea; Department of Pathology, Seoul National University College of Medicine, 103 Daehak-ro, Jongno-gu, Seoul 110-799, Republic of Korea. Electronic address: chungjh@snu.ac.kr.
Abstract
OBJECTIVES: Activating mutations in the epidermal growth factor receptor (EGFR) kinase domain are correlated with dramatic clinical responses in non-small cell lung cancer patients treated with EGFR-tyrosine kinase inhibitors (TKIs). The two most common EGFR mutations, representing 85-90% of EGFR mutations, are the E746_A750 deletion in exon 19 and the L858R point mutation in exon 21. We conducted this study to evaluate the suitability of mutation-specific antibodies that can detect E746_A750 deletion and L858R mutant EGFR proteins by immunohistochemistry (IHC). MATERIALS AND METHODS: In a cohort of consecutive patients with surgically resected lung adenocarcinomas (n=240), mutant EGFR protein expression was assessed by IHC using specific antibodies (clone SP111 and SP125) to the 2 major forms of EGFR mutations. Immunoreactivity was scored as 0-3, and the results were compared with the EGFR-mutational status. RESULTS: With a cutoff value of IHC 2+ for SP 111 (anti-EGFR E746_A750 del antibody) and SP 125 (anti-EGFR L858R antibody), both antibodies showed high specificity (99.0% and 89.7%, respectively) and sensitivity (70.6% and 80.4%, respectively). While cases with IHC scores of 3 using these 2 antibodies positively correlated with the EGFR-mutational status, cases with IHC scores lower than 3+ showed variable results regarding EGFR-mutational status. CONCLUSION: Although each antibody showed relatively high specificity, some EGFR-mutant cases were not detected by the mutation-specific antibodies. Various forms of exon 19 deletions, except E746_A750, were rarely detected by the mutant-specific antibody. Therefore, IHC-negative cases require further molecular analysis to confirm the presence of EGFR mutations.
OBJECTIVES: Activating mutations in the epidermal growth factor receptor (EGFR) kinase domain are correlated with dramatic clinical responses in non-small cell lung cancerpatients treated with EGFR-tyrosine kinase inhibitors (TKIs). The two most common EGFR mutations, representing 85-90% of EGFR mutations, are the E746_A750 deletion in exon 19 and the L858R point mutation in exon 21. We conducted this study to evaluate the suitability of mutation-specific antibodies that can detect E746_A750 deletion and L858R mutant EGFR proteins by immunohistochemistry (IHC). MATERIALS AND METHODS: In a cohort of consecutive patients with surgically resected lung adenocarcinomas (n=240), mutant EGFR protein expression was assessed by IHC using specific antibodies (clone SP111 and SP125) to the 2 major forms of EGFR mutations. Immunoreactivity was scored as 0-3, and the results were compared with the EGFR-mutational status. RESULTS: With a cutoff value of IHC 2+ for SP 111 (anti-EGFR E746_A750 del antibody) and SP 125 (anti-EGFRL858R antibody), both antibodies showed high specificity (99.0% and 89.7%, respectively) and sensitivity (70.6% and 80.4%, respectively). While cases with IHC scores of 3 using these 2 antibodies positively correlated with the EGFR-mutational status, cases with IHC scores lower than 3+ showed variable results regarding EGFR-mutational status. CONCLUSION: Although each antibody showed relatively high specificity, some EGFR-mutant cases were not detected by the mutation-specific antibodies. Various forms of exon 19 deletions, except E746_A750, were rarely detected by the mutant-specific antibody. Therefore, IHC-negative cases require further molecular analysis to confirm the presence of EGFR mutations.