FISH test for chronic lymphocytic leukaemia

You may have a range of blood tests to diagnose chronic lymphocytic leukaemia (CLL) and throughout treatment. These may include cytogenetic tests. Cytogenetic tests look at all the chromosomes in the leukaemia cells. Fluorescent in situ hybridisation (FISH) testing, is an important cytogenetic test that looks for specific changes in genes or chromosomes in the CLL cells.

FISH and cytogenetic testing give information about certain gene changes in chromosomes. The results tell your doctors how well certain drugs may work for you, and helps them plan your treatment.

Gene mutation tests check for important changes. For example, they may check if a gene called TP53 is missing or does not work.

TP53 is usually found in a part of chromosome 17 (called 17p). When this part of the chromosome:

• is missing (deleted), doctors call it a p53 deletion
• has changed (mutated), doctors call it a p53 mutation.

Fewer than 10% of people with CLL have a p53 deletion or p53 mutation when they are diagnosed. But it can develop over time and is more common in CLL that comes back after treatment. Because of this, and depending on your situation, these tests may be repeated.

CLL with a p53 deletion or p53 mutation does not usually respond well to standard chemotherapy treatment. Doctors use different types of targeted therapy drugs to treat this type of CLL. 

We have more information about how CLL is treated.