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

The clinicopathological features and genomic rearrangements of anaplastic lymphoma kinase (ALK) fusion cases have not been fully identified. 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). 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. 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. 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.