Fish test for chronic lymphocytic leukaemia

A FISH test looks for a small number of specific changes in genes or chromosomes in the chronic lymphocytic leukaemia (CLL) cells.

A FISH test looks for a small number of specific changes in genes or chromosomes in the chronic lymphocytic leukaemia (CLL) cells. It gives information about the gene changes in chromosomes, such as whether a part is missing or ‘deleted’. Information from these tests helps doctors know how well certain drugs may work. This helps them plan your treatment.

A blood sample is used for a FISH test for CLL.

Tests that look at changes in genes or chromosomes are called cytogenetic tests.

The most important change is when a gene called TP53 is missing or does not work. This can happen when part of chromosome 17 (17p), where the gene is usually found, is missing (deleted), or when the gene has changed (mutated). You may hear this called a ‘del 17p’. Often, doctors call this a ‘p53 deletion’, or ‘p53 mutation’.

Fewer than 1 in 10 (10%) people with CLL have a p53 deletion or p53 mutation when they are first diagnosed. But the deletion is more common in CLL that has come back after treatment.

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

We have more information about how CLL is treated.