What it is: The ALK gene encodes a receptor for tyrosine kinase on the cell surface. Binding to the receptor activates the RAF, RAS and MEK signaling pathways.
The result of this signaling is cell growth and cell proliferation.
Transpositions of ALK that bring it into conjugation with other genes (e.g., ALK-EML4) lead to overexpression of ALK as part of the chimeric protein.

Why the test is done: In non-small cell lung cancer, the presence of ALK translocation predicts sensitivity to tyrosine kinase inhibitors (TKIs) (e.g., Crizotinib, Ceritinib, Alectinib)

Frequency: Approximately 2% of non-small cell lung carcinomas.
More common in mucinous lung adenocarcinomas.
More common in non-smokers.
Less common in squamous cell carcinomas of the lung.