Every cell in your body contains chromosomes – strands of genes and other DNA that form the blueprint for how your body looks and works.
By examining your chromosomes up close, scientists can spot genetic (inherited) or acquired abnormalities that can signal the presence of cancer or other diseases. Those abnormalities may also predict the aggressiveness of the disease and help identify the treatments that will be most effective.
The process begins in the Clinical Cytogenetics Laboratory, where cells are cultured, stained, magnified and digitally photographed under a microscope. This provides a “group photo” of all 46 of your chromosomes – 22 inherited from each of your parents, plus the X and Y chromosomes that determine your gender – all scattered about as if spilled on a table. Working with the computerized image, lab technologists organize the chromosomes into pairs, matched according to such characteristics as size and the locations of the light and dark bands that are unique to each chromosome. Then the pairs are numbered, from 1 to 22 (See illustration at right).
The karyotype can be colorized with spectral karyotyping (SKY), or specific regions on chromosomes can be made to glow with fluorescence in situ hybridization (FISH).
The SKY and FISH techniques make it easier for scientists to flag abnormalities – for example, missing chromosomes, extra chromosomes, or “translocations,” in which a chromosomal region from one numbered pair switches places with another chromosomal region in a different pair. “We see specific chromosomal alterations in certain forms of cancer,” says AnneMarie Block, PhD, Director of Roswell Park’s Clinical Cytogenetics Laboratory.
"One example is chronic myeloid leukemia, a form of cancer in which pieces of chromosomes 9 and 22 switch places. Our job is to describe these abnormalities when we see them in patients. That information is joined with what the pathologist sees through the microscope, the clinical presentation of the patient, and the characteristics on the outside of the cells, in order to reach a diagnosis."
Cytogenetic analysis can also help identify the most promising treatments, because therapies have been developed to target specific chromosomal abnormalities.