I recently had my first FISH panel done after being diagnosed with CLL. I know it shows abnormalities in cancerous cells, but how exactly does it work, and how does it know which cells to isolate?
Bear with me — this is complicated. First, note that normal cells can accumulate mutations over time. Some mutations in the genes lead to more destruction of the genome (the term for all the genes in a cell). After a while, it's apparent that the genome is highly unstable, and entire large chunks of chromosomes may be moved from one location to another. FISH (fluorescent in situ hybridization) helps test what chunks have been moved where. During this process, certain genetic elements are "stained" with chemicals that make the DNA glow in different colors when special wavelengths of light are shone on it. In a genome in which the colors show up in the wrong locations, relative to other color markers, too many times (more than twice) or not at all (a chromosome segment is deleted entirely), FISH can help identify specific genetic defects.
After the hematopathologist (blood pathologist) obtains a specimen of your blood or bone marrow, it's used to make a microscope slide with a thin, single layer of cells. The hematopathologist then uses the colored markers to examine your cells. The specific aberrant location of the FISH color markers can help your oncologist/hematologist determine a prognosis and possibly treatment for your CLL.
There are too many known genetic defects in CLL to describe here. But I can give you a couple of examples: The 13q deletion (loss of an entire "arm" of the 13th chromosome) is associated with a very good prognosis because the median time for survival (that is, 50 percent survival) is almost 12 years from diagnosis. Contrast this with the 17p deletion, where median survival is historically only 3 years from the time of diagnosis. Based on your cytogenetics, as well as other factors, your doctors may recommend when it's best to consider treatment and how aggressive that treatment should be.
Learn more in the Everyday Health Leukemia Center.
Last Updated: 9/23/2010