Clinical significance of ROS1 5’ deletions in non-small cell lung cancer

Highlights

• NSCLC patients with ROS1 fusions are eligible for first-line therapy with Crizotinib.

• Diagnostic FISH criteria were mirrored from ALK, including tumors with 5’ deletions.

• Response to Crizotinib in patients with ROS1 deletions has never been investigated.

• We show that 5’ ROS1 deletions are linked with a chance of response to Crizotinib.

• Confirmation of ROS1 fusions NGS is beneficial to define the ROS1 fusion partners.

Abstract

Objectives

Patients harboring rearrangements of the ROS1 gene are eligible for first-line therapy with Crizotinib, which represents the best available treatment option. Diagnostic criteria, based on break-apart fluorescence in situ hybridization, were mirrored from ALK by analogy and include tumors with 5' deletions. However, the probability of response to Crizotinib in patients with 5' deletion in ROS1 is unknown given the rarity of this condition.

Materials and methods

We hereby describe clinical outcome of 8 NSCLC patients harboring a 5' deletion at FISH treated with Crizotinib

Results

Three out of 4 cases whose 5' deletion was confirmed by NGS as a ROS1/EZR fusion displayed an objective response to Crizotinib while a case with ROS1/SDC4 fusion did not. By contrast, among the 4 cases where NGS did not detect ROS1 gene fusions only 2 patients responded to crizotinib therapy with one also harboring a concomitant EML4-ALK rearrangement.

Conclusion

5' ROS1 deletions detected by FISH are associated with a high chance of response to Crizotinib in NSCLC, similarly to canonical ROS1 split-apart FISH rearrangements. However, the confirmation of the ROS1 gene fusion with at least another method, such as NGS, seems beneficial in order to define the ROS1 fusion partner and to avoid possible false positive results.

Introduction

The ROS1 gene is located on chromosome 6q22 and belongs to the insulin receptor family controlling proliferation through various cell pathways including STAT3 and PI3K/AKT/mTor. [1] Approximately 1–3% of non-small cell lung cancer (NSCLC) harbor ROS1 gene fusions, mainly with the CD74, EZR and the SCD4 genes, that are oncogenic. [1,2] Given the high sequence homology between ALK and ROS1 genes, inhibitors of the tyrosine kinase (TKI) catalytic domain of ALK can be utilized successfully also in tumors harboring ROS1 fusions. Therefore the use of Crizotinib has been approved for first-line therapy of NSCLC patients with confirmed ROS1 rearrangement. [3] Several methods including next-generation sequencing (NGS) can be utilized to assess ROS1 fusions. [4] Break-apart fluorescent in situ hybridization (FISH) still represents the gold standard method for the detection of ROS1 rearrangements on histological and cytological material. [5] This test is based on two probes specific for the 6q22 region. [6] In case of translocation between ROS1 and a partner gene, the FISH will show at least one split and one merged signal. Conversely, in case of 5’ deletion at the 6q22 region the FISH will reveal at least one merged signal and one single signal referred to the 3’ residual probe. Both the latter conditions are generally diagnosed as positive for gene fusion and lead to therapy with a TKI. NGS technologies can detect ROS1 fusions using imbalance assays after retro-transcription of fusion RNA transcript to cDNA and can provide information regarding the partner of the fusion. [7]

Objective tumor response to TKI in case of 5’ deletion at FISH has been reported for ALK-positive patients but not for ROS1 so far. Therefore, we have investigated the clinical and molecular significance of ROS1 5’ deletions in a consecutive series of patients with advanced NSCLC submitted to Crizotinib treatment