The anaplastic lymphoma kinase (ALK) rearrangement defines a distinct molecular subtype of non‐small cell lung cancer (NSCLC). Despite the excellent initial efficacy of ALK inhibitors in patients with ALK+ lung cancer, resistance occurs almost inevitably. To date, there is no reliable biomarker allowing the identification of patients at higher risk of relapse. Here, we analysed a subset of 53 ALK+ tumours with and without TP53 mutation and ALK+ NSCLC cell lines by NanoString nCounter technology. We found that the co‐occurrence of early TP53 mutations in ALK+ NSCLC can lead to chromosomal instability: 24% of TP53‐mutated patients showed amplifications of known cancer genes such as MYC (14%), CCND1 (10%), TERT (5%), BIRC2 (5%), ORAOV1 (5%), and YAP1 (5%). MYC‐overexpressing ALK+ TP53‐mutated cells had a proliferative advantage compared to wild‐type cells. ChIP‐Seq data revealed MYC‐binding sites within the promoter region of EML4, and MYC overexpression in ALK+ TP53‐mutated cells resulted in an upregulation of EML4–ALK, indicating a potential MYC‐dependent resistance mechanism in patients with increased MYC copy number. Our study reveals that ALK+ NSCLC represents a more heterogeneous subgroup of tumours than initially thought, and that TP53 mutations in that particular cancer type define a subset of tumours that harbour chromosomal instability, leading to the co‐occurrence of pathogenic aberrations. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Aims The advent of specific ALK‐targeting drugs has radically changed the outcome of patients with ALK translocated non‐small‐cell lung cancer (NSCLC). However, emerging resistance to treatment with ALK inhibitors in these patients remains a major concern. In previous studies, we analysed two ALK+ patient cohorts (TP53 wild‐type/TP53 mutated) in terms of copy number alterations. All patients belonging to the TP53 wild‐type group had mainly genetically stable genomes, with one exception showing chromosomal instability and amplifications of several gene loci, including TERT. Here, we aimed to determine the prevalence of TERT amplifications in these ALK+ lung cancer patients by analysing an independent cohort of 109 ALK translocated cases. We further analysed the copy numbers of numerous cancer‐relevant genes and other genetic aberrations. Methods and results The prevalence of TERT amplifications was determined by means of FISH analyses. Copy numbers of 87 cancer‐relevant genes were determined by NanoString nCounter® technology, FoundationOne® and lung‐specific NGS panels in some of these TERT‐amplified samples, and clinical data on patients with TERT‐amplified tumours were collected. Our data revealed that five (4.6%) of all 109 analysed ALK+ patients harboured amplification of TERT and that these patients had genetically unstable genomes. Conclusions Our preliminary study shows that ALK+ adenocarcinomas should be evaluated in the context of their genomic background in order to more clearly understand and predict patients' individual course of disease.