1p/19q codeletion analysis by FISH (Fluorescence In Situ Hybridization) is a molecular diagnostic technique used primarily in the diagnosis and classification of a type of brain tumor known as an oligodendroglioma. The presence or absence of a codeletion of the short arm of chromosome 1 (1p) and the long arm of chromosome 19 (19q) is a key genetic feature that distinguishes oligodendrogliomas and can provide important prognostic information. Here’s how 1p/19q codeletion analysis by FISH typically works:
- Sample Collection: A tissue sample, typically obtained through a brain biopsy or surgical resection, is collected from the patient. This tissue sample contains tumor cells.
- Tissue Preparation: The collected tissue sample is processed and prepared for FISH analysis. This may involve fixing the tissue and preparing thin sections on glass slides.
- FISH Probe Preparation: Specific DNA probes are designed to target the 1p and 19q regions of the chromosomes. These probes are labeled with fluorescent molecules that emit distinct colors when exposed to specific wavelengths of light. One probe is designed to bind to the 1p region, and another is designed to bind to the 19q region.
- Hybridization: The tissue sample is incubated with both the 1p and 19q DNA probes. If there is a codeletion of both 1p and 19q, meaning both regions are missing or deleted in the tumor cells, the corresponding DNA probes will bind to the remaining target sequences.
- Fluorescent Labeling: When the DNA probes bind to the target 1p and 19q gene sequences, they emit fluorescent signals in their respective colors.
- Imaging and Analysis: The tissue sample is examined under a fluorescent microscope, which can distinguish between the different fluorescent signals emitted by the 1p and 19q probes. The presence or absence of a codeletion is determined based on the patterns of fluorescence signals. If both 1p and 19q regions are deleted in the tumor cells, it indicates a codeletion.
The presence of a 1p/19q codeletion is considered a molecular hallmark of oligodendrogliomas and can aid in distinguishing these tumors from other types of brain tumors. Oligodendrogliomas with a 1p/19q codeletion tend to have a better response to certain treatments, such as chemotherapy with agents like PCV (procarbazine, lomustine, and vincristine), and a more favorable prognosis compared to those without the codeletion.
The results of 1p/19q codeletion analysis by FISH provide critical information for tumor classification and treatment planning for patients with oligodendrogliomas. The interpretation of these results should be conducted by experienced pathologists or molecular geneticists who are familiar with the clinical context and guidelines for brain tumor diagnosis. The results are often used in conjunction with other diagnostic and prognostic factors to develop individualized treatment strategies.
