Significance and evaluation of anaplastic lymphoma kinase by immunohistochemistry in non-small cell lung cancer

We used immunohistochemistry and reverse transcription polymerase chain reaction (RT-PCR) to evaluate anaplastic lymphoma kinase (ALK) protein expression and gene rearrangements, respectively, in 283 cases of wild-type epidermal growth factor receptor (EGFR) non-small cell lung cancer biopsy specimens. Immunohistochemistry was positive for ALK in 52 cases (18.4 %), and there was no significant difference in staining between various monoclonal antibodies (Roche ALK test kit, D5F3, p-ALK, and EML4-ALK). On RT-PCR, 36 cases (12.7 %) were positive for ALK. Immunohistochemistry and RT-PCR were both positive in 35 cases and both negative in 230 cases, and both have a high consistency (265/283, 93.6 %). Including 17 cases, immunohistochemistry was positive but RT-PCR was negative, and in one case, immunohistochemistry was negative but RT-PCR was positive. On fluorescence in situ hybridization (FISH) testing of these 18 cases, only three cases were positive (one RT-PCR was positive; two immunohistochemistry were positive). There is a high prevalence of ALK positivity in wild-type EGFR non-small cell lung cancer. Immunohistochemistry for the detection of ALK gene rearrangements was highly consistent with RT-PCR, and thus, it is a good screening tool but produces false positive results that necessitate further screening by RT-PCR or FISH.