The Vysis ALK Break Apart FISH probe can detect cells with the EML4-ALK translocation. This translocation results in a chimeric tyrosine kinase with potent oncogenic activity. A tumor with this translocaton may respond to therapy with a tyrosine kinase inhibitor (TKI).
Gene location: chromosome 2
Technology: FISH (fluorescent in-situ hybridization)
The break apart probe consists of 2 probes that flank the point where the break in the ALK gene occurs. Each probe has a different color. If there is no translocation then the 2 colors are adjacent to each other and appear “fused”. If there is a translocation then the 2 colors are separated and “broken apart”.
|
Nucleic Acid Probe |
Probe Color |
|
300 kb probe binding adjacent to the 3’ end of the ALK gene but not involving it |
orange |
|
442 kb probe that starts at the 3’ end of the ALK gene and runs along the gene towards the 5’ end |
green |
|
Status of Cell |
Number of Fused or Adjacent Signals |
Number of Single Green Signals |
Number of Single Orange Signals |
|
negative for translocation |
1 or more |
none |
none |
|
negative for translocation |
1 or more |
1 or more |
none |
|
positive for translocation |
0 or more |
1 or more |
1 or more |
|
positive for translocation |
1 or more |
none |
1 or more |
where:
• The orange and green signals must be separated by 2 or more signal diameters to be “broken apart”.
• A single nucleus may contain both fused/adjacent signals and broken apart signals (a malignant cell may have 2 or more copies of chromosome 2). The presence of 1 or more broken apart signals indicates that at least one translocation is present (“positive”).
• The presence of a single green without a corresponding orange signal (in a cell with at least one or more fused or adjacent signals) indicates a deletion of the ALK-binding probe and is counted as negative.
Initially 50 nuclei are counted.
|
Number of Nuclei Positive |
Number of Nuclei Negative |
Percent |
Translocation |
|
< 5 |
> 45 |
< 10% |
negative |
|
5 to 25 |
25 to 45 |
10 to 50% |
indeterminate |
|
> 25 |
< 25 |
> 50% |
positive |
If an indeterminate value is recorded, then an additional 50 nuclei are counted and the results of the 2 counts combined (50 + 50 = 100).
|
Number of Nuclei Positive |
Number of Nuclei Negative |
Percent |
Translocation |
|
< 15 |
> 85 |
< 15% |
negative |
|
>= 15 |
<= 85 |
>= 15% |
positive |
Specialty: Hematology Oncology, Surgery, general, Pulmonology
ICD-10: ,
