11Q23 MLL Rearrangement (FISH)

This test looks for a rearrangement in the MLL gene, also called KMT2A, located on chromosome 11 at a spot called 11q23. Using a technique called FISH, which lets the lab actually visualize the gene under fluorescent light, technicians can tell whether this region has broken off and joined with another chromosome. That kind of swap, or rearrangement, shows up in certain types of leukemia, particularly acute myeloid leukemia and acute lymphoblastic leukemia. It’s especially common in infant leukemias and in leukemias that develop after chemotherapy treatment for another cancer. The test is usually run on a bone marrow or blood sample, not something you’d get done as part of a routine checkup.

Who should get this test done?

This test may be recommended for:

●     Individuals newly diagnosed with acute myeloid or acute lymphoblastic leukemia
●     Infants under one year of age diagnosed with leukemia
●     Individuals who developed leukemia after previous chemotherapy treatment
●     Individuals whose leukemia doesn’t show the more common genetic markers
●     Individuals being evaluated for treatment planning or risk stratification
Why consider this test?

Knowing whether the MLL gene is rearranged actually changes how doctors approach treatment. This particular abnormality tends to be associated with a tougher prognosis, so identifying it early helps the medical team plan more aggressive or targeted therapy from the start rather than waiting to see how a standard approach plays out. It’s also useful for distinguishing between leukemia subtypes that might look similar under the microscope but behave very differently. In infants especially, this rearrangement turns up quite often, so testing for it has become a fairly standard part of the diagnostic workup. Beyond diagnosis, doctors sometimes use it later on too, to check for minimal residual disease after treatment has started.

More information

This test is typically just one part of a broader cytogenetic workup that includes routine chromosome analysis alongside the FISH study, since FISH alone can miss abnormalities outside its specific probe target. If a rearrangement is found, doctors will often want follow-up testing to pin down exactly which partner gene is involved, as there are dozens of possible combinations, and that detail can matter for treatment decisions.

Other names of the test

●     MLL gene rearrangement test
●     KMT2A rearrangement FISH
●     Chromosome 11q23 translocation test
●     Mixed lineage leukemia gene test
●     MLL break-apart FISH