On the relevance of a testing algorithm for the detection of ROS1-rearranged lung adenocarcinomas
Lénaïg Mescam-Mancini1, Sylvie Lantuéjoul2, Denis Moro-Sibilot3
1Département d'Anatomie et Cytologie Pathologiques, Pôle de Biologie et Pathologie, CHU Grenoble, France; Plateforme de Génétique Moléculaire des Tumeurs, Pôle de Biologie et Pathologie, CHU Grenoble, France.
Objectives:
ROS1 proto-oncogene translocations define a new molecular subgroup in non-small cell lung cancers (NSCLC) and are associated with a response to the MET/ALK inhibitor, crizotinib. These rearrangements are described in 0.9-1.7% NSCLC, in wild-type EGFR, KRAS and ALK ("triple negative") lung adenocarcinomas. Rapid and efficient identification of these alterations is thus becoming increasingly important.
Materials And Methods:
In this study, 121 triple negative lung adenocarcinomas were screened by both IHC with the ROS1 D4D6 antibody, and FISH using two commercially available ROS1 break-apart probes. To address a possible cross-reactivity of the ROS1 antibody with other protein kinase receptors, we screened 80 additional cases with known EGFR, KRAS, PI3KCA, BRAF, HER2 mutations or ALK-rearrangement.
Results:
We diagnosed 9 ROS1-rearranged adenocarcinomas, with both a positive FISH result (51-87% rearranged nuclei) and a positive IHC staining (2+/3+ cytoplasmic staining). Only one of the ROS1-positive FISH cases was characterized by a classical split pattern, the others showed a variant pattern, most commonly involving a loss of the 5' telomeric probe. Considering a positivity threshold of 2+ stained cells, the sensitivity of the ROS1 D4D6 antibody compared to FISH was 100% and the specificity 96.9%, as two HER2-mutated tumors were positive with D4D6 antibody, without any translocation in FISH. All the ROS1-positive cases were at an advanced stage, arising in never or light smokers. They were mainly solid cribriform and acinar adenocarcinomas, with signet ring cells noted in 5 cases, and calcifications in 3 cases. One positive case was an invasive mucinous carcinoma.
Conclusion:
Our results show that a screening algorithm based on an IHC detection of ROS1 fusion proteins, confirmed if positive or doubtful by a ROS1 break-apart FISH assay, is pertinent in advanced "triple negative" lung adenocarcinomas, since the prevalence of ROS1-positive cases in this selected population reaches 7.4% in our series.
Insights
Identifying ROS1 rearrangements in non-small cell lung cancer (NSCLC) is crucial for targeted therapy. Immunohistochemistry (IHC) combined with fluorescence in situ hybridization (FISH) provides an effective screening method for ROS1-positive "triple negative" lung adenocarcinomas.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- ROS1 proto-oncogene translocations represent a distinct molecular subtype of non-small cell lung cancer (NSCLC).
- These rearrangements are found in approximately 0.9-1.7% of NSCLC, specifically in tumors wild-type for EGFR, KRAS, and ALK (termed "triple negative").
- Identifying ROS1 rearrangements is critical for guiding treatment with targeted therapies like crizotinib.
Purpose of the Study:
- To evaluate the efficacy of a screening algorithm using immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) for detecting ROS1 rearrangements in NSCLC.
- To determine the prevalence of ROS1 rearrangements in a cohort of "triple negative" lung adenocarcinomas.
Main Methods:
- 121 "triple negative" lung adenocarcinomas were analyzed using IHC with the ROS1 D4D6 antibody and FISH with ROS1 break-apart probes.
- An additional 80 cases with known mutations or rearrangements in other relevant genes (EGFR, KRAS, PI3KCA, BRAF, HER2, ALK) were screened to assess antibody specificity.
Main Results:
- Nine cases of ROS1-rearranged adenocarcinomas were identified, confirmed by both positive FISH and IHC staining.
- The ROS1 D4D6 antibody demonstrated 100% sensitivity and 96.9% specificity compared to FISH, with variant FISH patterns observed in most positive cases.
- ROS1-positive tumors were predominantly found in advanced-stage disease among never or light smokers and exhibited specific histological features.
Conclusions:
- An integrated screening approach utilizing IHC for initial detection followed by FISH for confirmation is highly effective for identifying ROS1 rearrangements in advanced "triple negative" NSCLC.
- This diagnostic strategy identified ROS1 rearrangements in 7.4% of the selected patient population, highlighting its clinical relevance for targeted therapy selection.
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