Table 1 Assays for the detection of MET dysregulation

FISH

The MET gene copy numbers were obtained by detecting the sites of MET and CEP7 (as the control).

1. The ratio of MET vs. CEP7: low amplification (≥ 1.8, < 2.2), medium amplification (> 2.2, <5), and high amplification (≥ 5).

2. The proportion of positive cells in total cells.

Advantages: high accuracy; good repeatability; good correlation with the curative effect, and less specimens can be detected.

Disadvantages: fluorescence microscopy equipment and experienced operator are required; MET expressed on the cell surface but not amplified could not be detected.

ddPCR

Detecting the difference in fluorescence signal strength between the amplificated MET site and internal reference site.

MET gene amplification was defined by ddPCR as MET copy number > 5.5

Advantages: high accuracy and high detection speed.

Disadvantages: high requirement for DNA fragment quality.

IHC

Anti-c-MET (SP44) rabbit monoclonal antibody was used as the primary antibody and positive results were determined by evaluating the staining status of the cells.

2+ or 3+ is defined as high MET expression, and 0 or 1+ is defined as low MET expression (Metmab criteria).

3+ (≥ 50% tumor cells strongly positive), 2+ (≥ 50% tumor cells positive/weakly positive or < 50% tumor cells strongly positive), 1+ (weakly positive tumor cells ≥ 50% or positive cell number < 50%), and 0 (the number of tumor cells without staining or with any intensity staining < 50%).

Advantages: mature technology, rapid and simultaneous results in many cases, simultaneous observation of cell morphology, and low cost.

Disadvantages: the result interpretation is subjective; easy to be disturbed in the testing process.

NGS

CNV can be estimated by calculating the coverage (sequencing depth) of the region where the MET gene is located. The coverage area is divided into a continuous bin, and the final copy number given is the average of all bin of a gene.

The covering depth of more than 60% of the bin of a gene in cancer samples is significantly higher than the baseline level (z test), and the covering level of the entire gene region is statistically significant different from the baseline level (t test); the cutoff taken by different algorithms is different.

Advantages: multi-gene parallel detection can be achieved by tissue or blood detection, and all mutation, deletion, amplification, fusion, and other mutation types can be detected at one time, with high detection sensitivity.

Disadvantages: high testing cost, need NGS sequencing equipment, and high technical requirements.