A Novel, Highly Sensitive ALK Antibody 1A4 Facilitates Effective Screening for ALK Rearrangements in Lung Adenocarcinomas by Standard Immunohistochemistry

摘要

The identification of aberrantly activated tyrosine kinases in subsets of non-small-cell lung cancer (NSCLC) together with the development of specific kinase inhibitors has provided a major breakthrough in lung cancer therapy. Genomic rearrangements of the anaplastic lymphoma receptor tyrosine kinase (ALK) gene result in the formation of fusion proteins containing the ALK kinase domain.1'2 As a consequence, downstream signaling pathways implicated in cell growth and proliferation are constitutively activated. In lung adenocarcinoma, signaling of the activated tyrosine kinase can effectively be inhibited by the ALK inhibitor crizotinib.3'4 Patients with vlLK-rearranged tumors who benefit from treatment, however, merely represent 3%-6 % of adenocarcinoma patients,5 and reliable preselection by clinical or histopathological criteria hitherto is not possible. Given the high incidence of lung carcinoma, rapid screening for the identification of those few NSCLC patients with ALK rearrangements is desirable. Thus, the development of robust and reliable but also rapid and cost-effective laboratory tests is of importance. Currently, fluorescence in-situ hybridization (FISH) is the only approved diagnostic test to detect ALK rearrangement which, however, requires specialized technical equipment, expertise and is a low-throughput approach. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis reliably identifies ALK rearrangements by detecting unbalanced ALK transcript expression,6 but is not readily available as a routine method. Immunohistochemistry (IHC) is relatively inexpensive, rapid, and perfectly adapted for routine pathology practice, therefore representing a promising candidate for a screening test. However, reliable detection of the low ALK protein expression in AL^-rearranged NSCLC turned out to be difficult. Depending on the affinity of the antibody, the sensitivity of the detection system, the scoring system, and the experience of the scorer ALK immu-nostaining yields variable results. Substantial improvement was achieved by employing high affinity antibodies such as D5F3 and 5A4 in combination with sensitive detection methods.7"9