Background: Immunohistochemistry has been proposed as a specific and sensitive method to identify EGFR mutations or ALK rearrangements in lung tumours.
Patients and methods: We assessed EGFR and KRAS by direct sequencing in 154 patients with lung adenocarcinoma. ALK rearrangements were assayed by FISH and RT-PCR. Immunohistochemistry was carried out and evaluated closely following published methods using recommended monoclonal rabbit or mouse antibodies.
Results: Thirteen of 36 exon 19 EGFR-mutated tumours (36%)-including 12 of 22 with p.Glu746_Ala750del (55%)-were positive with the 6B6 antibody that was raised against p.Glu746_Ala750del. One hundred eleven of 114 EGFR exon 19 wild-type tumours (97%) were negative with 6B6. Four of 21 exon 21 EGFR-mutated tumours (19%)-including 4 of 17 with p.Leu858Arg (24%)-were positive with the 43B2 antibody that was raised against p.Leu858Arg. One hundred twenty-two of 124 (98%) EGFR exon 21 wild-type tumours were negative with 43B2. Two of four ALK rearrangements-including two of three with ELM4-ALK fusion transcripts-were identified with the 5A4 antibody. Eleven of 13 tumours without ALK rearrangement (85%) were negative with 5A4.
Conclusions: Immunohistochemistry is a specific means for identification of EGFR mutations and ALK rearrangements. It suffers, however, from poor sensitivity.