In situ fluorescence hybridization (FISH) is the latest method to determine the location of a genetic material in a cell up to individual genes and gene segments.
Since the FISH test can detect genetic abnormalities that cause cancer, it is an effective method for diagnosing some types of cancer. The test is also used to confirm the diagnosis and allows you to get additional information about the possible outcome of the illness and the feasibility of using chemotherapy.
For example, in patients with breast cancer, the FISH test of tissue taken during a biopsy helps to determine the presence of copies of the HER2 gene in the cells.
HER2 gene copy cells have more HER2 receptors that receive signals that stimulate the growth of cancer cells in the mammary gland. Therefore, for patients with copies of the HER2 gene, it is advisable to use Herceptin (trastuzumab) - a means that suppresses the ability of the HER2 receptors to receive signals.
Due to the high cost and relative inaccessibility of the FISH test, another test for the detection of breast cancer - immunohistochemistry (IGH) is used more often.
Disputes over the high efficiency of the FISH test are in the medical circles as compared to standard tests. However, thanks to technical progress, the FISH test is becoming cheaper and more affordable in a variety of clinical settings.
How does the FISH test work?
When conducting a FISH test on a patient's tissue sample, fluorescence labels are used that bind only to certain areas of the chromosome. Then, using a fluorescence microscope, determine the areas of the chromosomes with which the fluorescence probes are contacted, and the presence of possible abnormalities that provoke cancer development.
Cancer cells may show the following abnormalities:
- Translocation - the transfer of a chromosome region to a new position on the same or another chromosome;
- Inversion - the turn of the chromosome region by 180 degrees while maintaining the connection with the chromosome itself;
- Deletion - loss of part of the chromosome;
- Duplication - doubles the area of the chromosome, resulting in excessive content of copies of the gene in the cell.
Translations help diagnose some types of leukemia, lymphomas and sarcomas. The presence of duplication in breast cancer cells helps the physician to find optimal treatment.
The advantage of the FISH test against standard cytogenetic tests (investigating the genetic composition of cells) is that it allows you to identify even the smallest genetic changes that can not be considered with a conventional microscope.
Another important difference between the FISH test is the ability to carry it out in cells that have not yet begun to actively develop. Other tests are performed on cells only after their growth in the laboratory for two weeks, so the whole process can take up to three weeks, and the results of the FISH test become known in a few days.
Examples of a FISH test for cancer diagnosis
Although the FISH test is most often used to analyze genetic abnormalities in breast cancer, it also helps to get important information about other types of cancer.
For example, in the diagnosis of bladder cancer, the FISH urine cell test gives more accurate results than tests for atypical cells. In addition, it allows to determine the recurrence of bladder cancer for 3-6 months earlier.
The FISH test also helps detect lesions in the chromosomes with leukemia, including cells that indicate an aggressive form of chronic lymphocytic leukemia (CLL). Patients with an aggressive CLL may require urgent treatment, while in less aggressive forms, observation can be sufficient.
Disputes about the FISH test
Not all experts agree that the FISH test is the most accurate analysis for the diagnosis of cancers susceptible to herceptin.
In 2010, researchers from the Mayo Institute (Ireland) said that a less expensive IGC test is almost as effective for determining receptor susceptibility as the FISH test.
Other experts criticize the FISH test for the impossibility of detecting small mutations, such as small deletions, insertions, and point mutations, as well as ignoring some inversions.
Improve FISH Test
Despite the fact that FISH test technology allows to analyze not all areas of chromosomes, it is constantly developing in this direction.
For example, in 2007, Canadian scientists announced the development of a microscope microscope sized chip that would allow the FISH test to be carried out using a device in the palm of the hand.
This advanced test, called "FISH Chip Test", will allow you to get results within one day and will be cheaper than other tests.