Overview

ROS1 fusion FISH testing identifies the ROS1 gene rearrangement that defines a small but important subset of non-small-cell lung cancer patients eligible for ROS1-directed therapy. For distributors serving molecular diagnostics labs, the test's value is precise patient selection: only a few percent of lung tumors carry the fusion, so accurate screening avoids treating the wrong population. This article covers who should be tested and how FISH confirms the fusion.

How It Works

Fluorescence in-situ hybridization uses labeled DNA probes that bind the ROS1 locus on chromosome 6. When a rearrangement is present, the signal pattern shows a split or co-localization distinct from the normal pair, read by a trained cytogeneticist under a fluorescence microscope. The method directly visualizes the genomic event, which remains the established confirmation approach even as sequencing platforms expand their fusion menus.

Indications

Testing is recommended for advanced non-small-cell lung cancer, particularly adenocarcinoma, where a ROS1-directed agent is planned. It is most informative when started early so the eligible minority is not missed. Buyers should position the assay alongside broader profiling rather than as a replacement, because many patients need several marker results before a regimen is fixed.

Dosage & Administration

The assay runs on a fixed tissue section; laboratories should specify fixation, section thickness, and the minimum tumor area required for a reliable read. Turnaround is usually several working days. Reports should state the percentage of positive cells and the signal pattern, because payers and prescribers expect that detail for approval and for selecting the appropriate targeted agent.

Storage & Sourcing

Probe kits and reagents are light- and temperature-sensitive and must be shipped and stored under validated 2 to 8°C conditions with logging. Source from suppliers offering probe validation data, positive-control slides, and training. Confirm minimum order quantities suit the lab's monthly test volume and whether the probes are licensed for the intended diagnostic use in the destination market.

Procurement teams should confirm the supplier ships positive and negative control slides with each lot so the laboratory can verify reader performance before any patient sample is interpreted and reported to the prescriber.

Laboratories should record the reader identity and the microscope configuration used for each batch so FISH results remain reproducible across shifts and sites.

FAQ

Q: Which lung cancer patients should receive ROS1 FISH first? Q: Does a positive FISH result guarantee response to ROS1 therapy? Q: How many positive cells confirm a true fusion? Q: Can sequencing replace FISH for ROS1 detection?