ALK rearranged NSCLC is the subtype defined by structural rearrangement of the anaplastic lymphoma kinase (ALK) gene, most often fused with the EML4 gene on chromosome 2p. It accounts for 3-7% of NSCLC. The EML4-ALK fusion was first described in lung cancer in 2007, and the 2011 approval of the first ALK inhibitor crizotinib marked the beginning of the molecular treatment era. The typical clinical profile includes younger age (median around 50), never-smoker (about 60%) or light-smoker status, adenocarcinoma histology, Asian or Caucasian ancestry, and a high incidence of brain metastases (30-40% at diagnosis). The clinical profile resembles EGFR mutant NSCLC, although the molecular drivers differ.
ALK fusions place the kinase in a constitutively active state, leading to sustained signaling through downstream pathways (RAS/MAPK, PI3K/AKT/mTOR, STAT3). Detection methods include: (1) FISH (fluorescence in situ hybridization) — the historical gold standard; (2) IHC (immunohistochemistry) — a sensitive and rapid screening method using the D5F3 antibody; (3) NGS (next-generation sequencing) — identifies the fusion partner and exon breakpoint. EML4-ALK is the most common partner (85%), but KIF5B-ALK, TFG-ALK, and STRN-ALK are also recognized. Each ALK TKI faces different resistance mutations: L1196M (gatekeeper, crizotinib resistance), G1269A, C1156Y, F1174C, and G1202R (which can also resist lorlatinib). Each new generation TKI is engineered to overcome the resistance spectrum of its predecessors.
Treatment evolution and current approach: First-generation crizotinib also targets ROS1 but has limited CNS penetration and a 10-12 month PFS. Second-generation drugs — ceritinib, alectinib, brigatinib — offer better potency and CNS penetration. Alectinib's superiority over crizotinib in the first line was confirmed by ALEX and J-ALEX (PFS 34.8 vs 10.9 months), and brigatinib showed similar efficacy in ALTA-1L. Third-generation lorlatinib covers the broadest resistance mutation spectrum with excellent CNS penetration; CROWN reported a PFS three times longer than crizotinib in the first line (3-year OS 67% vs 41%). Today's standard is first-line alectinib or brigatinib; lorlatinib is an alternative and a first-line option in some centers. After resistance: repeat biopsy plus NGS to choose the next TKI based on the resistance mutation; combine with CNS-directed radiotherapy (SRS) when needed; chemotherapy is reserved for later lines. Immunotherapy is generally ineffective in ALK+ NSCLC (low TMB, low PD-L1, immune-excluded TME).