EML4-ALK lung cancer inv(2)
46,XY,inv(2)(p21p23)
Also known as: EML4-ALK, ALK-positive lung cancer, ALK rearrangement, inv(2)
46,XY,inv(2)(p21p23) is the paracentric inversion behind ALK-positive lung cancer, fusing EML4 with ALK within the short arm of chromosome 2. Typically found in younger patients and never or light smokers, it is the target of crizotinib and the ALK inhibitors that followed.
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What banding sees: The inversion within 2p is far too small to see with banding, so ALK-positive lung cancer is diagnosed by FISH, immunohistochemistry or sequencing rather than by a karyotype. The drawing above shows where the missing segment lies, not what would be visible down a microscope.
What the notation means
46- total chromosome count (the normal human number)
XY- sex chromosomes: one X, one Y (usual male karyotype)
inv(2)(p21p23)- an INVERSION in chromosome 2: the segment between 2p21 and 2p23 is flipped end-for-end (paracentric, within one arm)
Clinical notes
inv(2)(p21p23), EML4::ALK lung adenocarcinoma
EML4::ALK. Non-small cell lung cancer, typically adenocarcinoma. The rearrangement behind ALK-positive lung cancer: a short paracentric inversion within 2p, far too small to see on banding, so it is a FISH, immunohistochemistry or sequencing finding and the notation is taught rather than observed. A few per cent of non-small cell lung cancer, typically younger patients and never or light smokers, and treatable with crizotinib and the ALK inhibitors after it. The same ALK is the t(2;5) partner in anaplastic large cell lymphoma.