BackgroundRecently Echinoderm microtubule-associated protein-like 4- anaplastic lymphoma kinase (EML4-ALK) fusion gene has become an important biomarker for ALK tyrosine kinase inhibitor (crizotinib) treatment in NSCLC. However, the best detection method and the significance of EML4-ALK variant types remain uncertain.MethodsReverse transcriptase-polymerase chain reaction (RT-PCR), fluorescence in Situ hybridization (FISH) and Immunohistochemical (IHC) stain were performed on tumor tissues of 312 NSCLC patients for detection of ALK rearrangements. Mutation analyses for EGFR and KRAS genes were also performed.ResultsThirteen of the 312 patients (4.17%) had ALK rearrangements detected by RT-PCR. If RT-PCR data was used as the gold standard, FISH tests had a low sensitivity (58.33%), but very good specificity (99.32%). IHC stain had better sensitivity (91.67%) than FISH, but lower specificity (79.52%), when the cut off was IHC2+. All of the 8 patients with high abundance of EML4-ALK positive cells in tumor tissues (assessed by the signal intensities of the RT-PCR product), were also have high expression of ALK protein (IHC3+), and positive for FISH, except one failed in FISH. Variants 3a+3b (4/5, 80%) of EML4-ALK fusion gene were more common to have high abundance of EML4-ALK positive cells in tumor tissues than variant 1 (1/3, 33.3%). Meta-analysis of the published data of 2273 NSCLC patients revealed that variant 3 (23/44, 52.3%) was the most common type in Chinese population, while variant 1 (28/37, 75.7%) was most common in Caucasian.ConclusionsAmong the three detection methods, RT-PCR could detect not only the presence of EML4-ALK fusion gene and their variant types, but also the abundance of EML4-ALK positive cells in NSCLC tumor tissues. The latter two factors might affect the treatment response to anti-ALK inhibitor. Including RT-PCR as a diagnostic test for ALK inhibitor treatment in the prospective clinical trials is recommended.
Background:Recently the echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK) fusion gene with transforming activity was identified in non-small cell lung cancer (NSCLC). In addition, NSCLC patients with the EML4-ALK fusion gene had a dramatic response and longer progression free survival after ALK inhibitor treatment than those without this fusion gene. However, the incidence and clinical and molecular characteristics of the EML4-ALK fusion gene in NSCLC patients of Taiwan are still unclear. Methods:Sixty-four fresh frozen tumor specimens were obtained from the tissue bank of Chang Gung Memorial Hospital for RNA extraction and EML4-ALK fusion gene detection. Paraffin sections of lung tumors from all of these patients were available and were analyzed for ALK protein expression by immunohistochemical (IHC) study. The results were correlated with clinical and molecular biomarkers. Results:Three of the 64 tumors (4.7%) had the EML4-ALK fusion gene. Two were adenocarcinomas, and one was adenosquamous carcinoma. Twenty patients with non-squamous cell carcinomas had epidermal growth factor receptor (EGFR) mutations, so the EML4-ALK fusion gene was found in 14.3% of EGFR wild type non-squamous cell carcinomas. Two tumors were variant 3 (3a+3b with 3b predominant) and had strong staining (3+) for ALK by IHC stains. One tumor was variant 1 and had moderate staining (2+) for ALK. None of the ALK wild type tumors had strong staining for ALK. When compared with other clinical and molecular features, only the IHC stain for ALK was significantly correlated with the EML4-ALK fusion gene (p = 0.0002). Conclusions: ALK overexpression detected by IHC study could be a promising detection method for the EML4-ALK fusion gene and is worth further confirmation with more samples.
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