What is Fluorescent In Situ Hybridization (FISH)?
Fluorescent In Situ Hybridization (FISH) is a powerful molecular technique used to detect and localize the presence or absence of specific DNA sequences on chromosomes. This is achieved by using fluorescently labeled DNA probes that bind to complementary DNA sequences in a sample. The resulting fluorescence can be analyzed under a fluorescence microscope, allowing for the visualization of genetic abnormalities at the chromosomal level.
How is FISH Used in Cancer Diagnosis?
FISH is widely used in cancer diagnosis to identify chromosomal abnormalities that are often associated with various types of cancer. For example, FISH can detect gene amplifications, deletions, and translocations that are key drivers in the development and progression of cancers such as breast cancer, lung cancer, and leukemia. By identifying these genetic changes, FISH helps in the accurate diagnosis and classification of cancers, guiding treatment decisions.
Sensitivity and Specificity: FISH is highly sensitive and specific, making it possible to detect even small genetic changes that other techniques might miss.
Visualization: FISH allows for the direct visualization of genetic abnormalities within the context of the cell, providing spatial information that is crucial for understanding the nature of the genetic change.
Versatility: FISH can be used on a variety of sample types, including fresh, frozen, and formalin-fixed paraffin-embedded (FFPE) tissues.
Quantification: FISH can quantify the number of gene copies, providing important information about gene amplification or deletion.
Resolution: While FISH can detect large-scale chromosomal changes, it may not be as effective in identifying small-scale mutations or single nucleotide polymorphisms (SNPs).
Cost and Complexity: FISH can be expensive and requires specialized equipment and expertise, which may limit its availability in some settings.
Interpretation: The interpretation of FISH results can be complex and may require experienced personnel to ensure accurate analysis.
HER2 Testing: In breast cancer, FISH is used to detect the amplification of the HER2 gene, which can guide the use of targeted therapies such as trastuzumab.
ALK Rearrangement: In non-small cell lung cancer (NSCLC), FISH is used to identify ALK gene rearrangements, which can indicate the potential benefit of ALK inhibitors.
Chromosomal Translocations: In leukemias and lymphomas, FISH is used to detect specific chromosomal translocations, such as the BCR-ABL fusion gene in chronic myeloid leukemia (CML).
Sample Preparation: Cells or tissue samples are prepared and fixed on a microscope slide.
Probe Hybridization: Fluorescently labeled DNA probes are applied to the sample and allowed to hybridize to their complementary DNA sequences.
Washing: Excess probes are washed away, leaving only the probes that have bound to their target sequences.
Visualization: The sample is examined under a fluorescence microscope, and the fluorescent signals are analyzed to identify genetic abnormalities.
Multiplex FISH: This technique allows for the simultaneous detection of multiple genetic targets in a single assay, increasing the amount of information obtained from a single sample.
Automated FISH: Automation of the FISH process can improve throughput and consistency, making the technique more accessible and efficient.
Digital FISH: Digital imaging and analysis tools are being developed to improve the accuracy and ease of interpreting FISH results.
