Assessment of a New ROS1 Immunohistochemistry Clone (SP384) for the Identification of ROS1 Rearrangements in Patients...

Area of Science:

• Oncology
• Molecular Pathology
• Biomarker Discovery

Background:

• ROS1 gene rearrangements are critical biomarkers in non-small cell lung cancer (NSCLC).
• Current guidelines recommend ROS1 immunohistochemistry (IHC) as a screening method, followed by confirmatory testing (FISH or molecular).
• Real-world data on novel IHC antibodies for ROS1 testing is essential.

Purpose of the Study:

• To evaluate the performance of a novel anti-ROS1 IHC antibody (clone SP384) in a large, multicenter NSCLC cohort.
• To compare the diagnostic accuracy of the SP384 clone with existing IHC methods and fluorescence in situ hybridization (FISH).

Main Methods:

• A total of 43 ROS1 FISH-positive and 193 ROS1 FISH-negative NSCLC samples were analyzed.
• Specimens were screened using two anti-ROS1 IHC antibodies (SP384 and D4D6) and compared against break-apart FISH.
• FISH-positive samples underwent next-generation sequencing for further molecular characterization.

Main Results:

• The SP384 clone achieved optimal cutoff values of an H-score ≥150 or ≥70% tumor cells with 2+ intensity, yielding 93% sensitivity and 100% specificity.
• The D4D6 clone demonstrated comparable results with 91% sensitivity and 100% specificity using an H-score ≥100.
• ROS1 expression in normal lung tissue was more frequent with SP384 (p < 0.0001), and the EZR-ROS1 variant correlated with membranous staining and specific FISH patterns.

Conclusions:

• The novel SP384 anti-ROS1 IHC antibody exhibits excellent sensitivity and specificity for detecting ROS1 rearrangements in NSCLC.
• SP384 serves as a valuable and reliable analytical option within the established ROS1 testing algorithm.
• This antibody supports efficient screening for ROS1 alterations, aiding in personalized NSCLC treatment strategies.