Let’s Go FISH-ing! | Aplastic Anemia and MDS International Foundation

Let’s Go FISH-ing!

Original Publication Date: 
Thursday, August 30, 2018
Article Source: 
Web Content

The recent emergence of targeted therapies has revolutionized the understanding and treatment of some bone marrow failure diseases, particularly myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). 

Targeted therapies are treatments that work by targeting specific genes or proteins to help stop cancer from progressing. It is different from chemotherapy, which affects all fast-growing cells at once. These therapies are made possible due to new medical technologies and diagnostic testing methods such as FISH.

What is FISH?

Fluorescence in situ hybridization (also known as FISH) is a cytogenetic (chromosomal) analysis that uses fluorescent dyes that attach to specific parts of the chromosomes and can detect changes in blood cancer cells. This method is used by pathologists when genetic abnormalities are not apparent under the microscope and is commonly used to obtain faster results of {for/on] diseases that have specific treatments. It also provides additional information about the cells’ behavior in comparison to what has been observed in the past in people with the same diagnosis and similar genetic changes.  FISH can be performed by using a blood sample or bone marrow cells.

What type of chromosomal abnormalities are reflected?

There are four major types of abnormalities found in chromosomes that will appear through FISH:

  • Portion of the chromosome is missing.
  • Part of the chromosome has been copied and the cell contains too many copies.
  • Part of a chromosome has broken off, turned upside down, and reattached in which the genetic sequence is inverted.
  • Insertion: Part of the chromosome breaks off and reattaches itself to another chromosome
  • Segments of two chromosomes are exchanged and reattached. This type of abnormality is typically the most common in helping doctors identify some types of leukemias, lymphomas, and sarcomas.

Why FISH?

The major advantage of FISH is that the results are usually available from the lab within a few days. By comparison, other cytogenetic tests which take about 2 weeks. these other methods require the cells to actively divide and grow in lab dishes before they can be tested.

How is FISH being used in the diagnosis and treatment of bone marrow failure diseases?

FISH has been the pioneer in the discovery of clonal chromosomal abnormalities in MDS. However, these are more frequently observed in 80% of patients with secondary MDS (MDS resulting from prior cancer treatment) vs. 40-60% of patients diagnosed with primary (de novo) MDS. 

The most common chromosomal abnormalities associated with MDS include: del(5q), del(7q), del(13q), del(20q), inv(3) and +8. These and other cytogenetic abnormalities are listed in the Revised International Prognostic Scoring System (IPSS-R) which helps doctors forecast prognosis and decide which treatment would be best for the patient.

FISH has also become a pivotal tool in the diagnosis and monitoring of chronic myeloid leukemia (CML). In CML, FISH is used to find the BCR-ABL gene. This gene develops as a direct result of the translocation between chromosomes 22 and 9, also known as the Philadelphia (Ph) chromosome. 

FISH is a significant advance in helping to get one step closer to finding cures. We look forward to seeing more improvements and innovations in diagnostic testing that lead to more personalized treatment for bone marrow failure diseases.