Clinicopathological Features of ALK Expression in 9889 Cases of Non-small-Cell Lung Cancer and Genomic Rearrangements Identified by Capture-Based Next-Generation Sequencing: A Chinese Retrospective Analysis

Background The clinicopathological features and genomic rearrangements of anaplastic lymphoma kinase ( ALK ) fusion cases have not been fully identified. Objective Our objective was to explore the status of ALK in non-small-cell lung cancer (NSCLC) specimens, to explore the relationships between ALK status and clinicopathological features and to identify genomic rearrangements via capture-based next-generation sequencing (NGS). Methods We tested 9889 NSCLC specimens for ALK status using the Ventana anti-ALK (D5F3) antibody. Clinicopathological features were analyzed and genomic rearrangements identified using capture-based NGS in 76 ALK-positive cases. Results In total, 485 specimens (4.90%) tested positive for ALK. The positivity rate was higher for adenocarcinoma samples than for non-adenocarcinoma samples (6.03 vs. 1.47%; p < 0.001) and for biopsies/cell blocks than for surgical specimens (7.00 vs. 4.16%; p < 0.001). Patient age, patient sex, specimen type, specimen histotype, and patient smoking history were all significantly correlated with ALK status. Genomic rearrangements were detected in 98.68% (75/76) of the ALK-positive samples; 89.33% (67/75) carried the canonical EML4-ALK , and the remaining samples carried only noncanonical ALK rearrangements. Four of these noncanonical ALK fusion samples were identified as carrying EML4-ALK transcripts at the RNA level. A novel fusion variant, SRD5A2-ALK , was revealed. Conclusions Younger patients with NSCLC, especially those aged < 30 years, were more likely to test positive for ALK. Positive ALK test results were more common in patients with invasive mucinous adenocarcinoma and solid-predominant invasive adenocarcinoma than in patients with other histotypes. Samples that carried only noncanonical ALK rearrangements may also have carried the canonical EML4-ALK, which was not detected by capture-based NGS. EML4-ALK transcripts might result from rare splicing mechanisms without genomic rearrangements.