ROS1 fusions in resected stage I-III adenocarcinoma: Results from the European Thoracic Oncology Platform Lungscape project

Lung Cancer. 2024 Aug:194:107860. doi: 10.1016/j.lungcan.2024.107860. Epub 2024 Jun 26.

Abstract

Background: ROS1 fusion is a relatively low prevalence (0.6-2.0%) but targetable driver in lung adenocarcinoma (LUAD). Robust and low-cost tests, such as immunohistochemistry (IHC), are desirable to screen for patients potentially harboring this fusion. The aim was to investigate the prevalence of ROS1 fusions in a clinically annotated European stage I-III LUAD cohort using IHC screening with the in vitro diagnostics (IVD)-marked clone SP384, followed by confirmatory molecular analysis in pre-defined subsets.

Methods: Resected LUADs constructed in tissue microarrays, were immunostained for ROS1 expression using SP384 clone in a ready-to-use kit and Ventana immunostainers. After external quality control, analysis was performed by trained pathologists. Staining intensity of at least 2+ (any percentage of tumor cells) was considered IHC positive (ROS1 IHC + ). Subsequently, ROS1 IHC + cases were 1:1:1 matched with IHC0 and IHC1 + cases and subjected to orthogonal ROS1 FISH and RNA-based testing.

Results: The prevalence of positive ROS1 expression (ROS1 IHC + ), defined as IHC 2+/3+, was 4 % (35 of 866 LUADs). Twenty-eight ROS1 IHC + cases were analyzed by FISH/RNA-based testing, with only two harboring a confirmed ROS1 gene fusion, corresponding to a lower limit for the prevalence of ROS1 gene fusion of 0.23 %. They represent a 7 % probability of identifying a fusion among ROS1 IHC + cases. Both confirmed cases were among the only four with sufficient material and H-score ≥ 200, leading to a 50 % probability of identifying a ROS1 gene fusion in cases with an H-score considered strongly positive. All matched ROS1 IHC- (IHC0 and IHC1 + ) cases were also found negative by FISH/RNA-based testing, leading to a 100 % probability of lack of ROS1 fusion for ROS1 IHC- cases.

Conclusions: The prevalence of ROS1 fusion in an LUAD stage I-III European cohort was relatively low. ROS1 IHC using SP384 clone is useful for exclusion of ROS1 gene fusion negative cases.

Keywords: Lung adenocarcinoma; Lungscape; NSCLC; ROS1.

MeSH terms

  • Adenocarcinoma of Lung* / genetics
  • Adenocarcinoma of Lung* / metabolism
  • Adenocarcinoma of Lung* / pathology
  • Adenocarcinoma of Lung* / surgery
  • Adult
  • Aged
  • Biomarkers, Tumor / genetics
  • Biomarkers, Tumor / metabolism
  • Europe
  • Female
  • Humans
  • Immunohistochemistry
  • In Situ Hybridization, Fluorescence
  • Lung Neoplasms* / genetics
  • Lung Neoplasms* / metabolism
  • Lung Neoplasms* / pathology
  • Lung Neoplasms* / surgery
  • Male
  • Middle Aged
  • Neoplasm Staging*
  • Oncogene Proteins, Fusion / genetics
  • Oncogene Proteins, Fusion / metabolism
  • Protein-Tyrosine Kinases* / genetics
  • Protein-Tyrosine Kinases* / metabolism
  • Proto-Oncogene Proteins* / genetics
  • Proto-Oncogene Proteins* / metabolism

Substances

  • ROS1 protein, human
  • Proto-Oncogene Proteins
  • Protein-Tyrosine Kinases
  • Biomarkers, Tumor
  • Oncogene Proteins, Fusion