Table 1.

Advantages and limitations of available diagnostic techniques for ROS1 rearrangement detection.

	IHC	(RT)-PCR	FISH	NGS
Advantages	Effective screening tool Reduction of costs avoiding unnecessary FISH test Short turnaround time	High specificity and sensitivity Short turnaround time	Low input of material High specificity and sensitivity Short turnaround time Does not require knowledge of possible fusion partners	Simultaneous testing of many predictive biomarkers, saving time and material High specificity and sensitivity Identification of several ROS1 fusion partners Both DNA and RNA as input material Recent validation of panels for ctDNA
Limitations	Lack of globally accepted scores May be difficult to interpret (background ROS1 expression on pneumocytes and alveolar macrophages)	Variable rates of failure (RNA integrity could be affected by fixation) Primers require knowledge of possible fusion partners Missing of uncommon or rare partners	Difficult to interpret (expertise of pathologist is needed) ROS1 fusion partners are not specified	Longer turnaround time Reduced sensitivity of DNA-based assays in detection of rearrangements Possible RNA failure in RNA-based assays