Fluorescence In Situ Hybridization (FISH)

FISH is a laboratory test that uses fluorescent DNA probes to detect specific genetic changes inside cells under a microscope. In suspected mesothelioma, it is most often used to look for deletion of a gene called CDKN2A (also called p16) on chromosome 9p21, which helps distinguish cancer from benign reactive cells.

Origin

FISH was developed in the early 1980s by Pinkel, Gray, and colleagues at the University of California, building on earlier radioactive in situ hybridization methods. It became a routine clinical tool in the 1990s as fluorescent probes for specific chromosomal regions became commercially available.

Significance in Asbestos Context

One of the hardest problems in diagnosing mesothelioma is telling malignant mesothelial cells apart from benign reactive ones, especially in pleural fluid or small biopsies. A FISH test showing homozygous deletion of CDKN2A (9p21) strongly supports a diagnosis of mesothelioma, and is now recommended in international diagnostic guidelines alongside BAP1 immunostaining. For patients, a confirmed FISH result can shorten the time to a definitive diagnosis, support eligibility for clinical trials, and provide objective molecular evidence in a legal claim that the disease is truly mesothelioma rather than a benign asbestos-related condition.

Example Sentence

The pathologist ordered a FISH test on the pleural biopsy, and the homozygous deletion of CDKN2A confirmed mesothelioma after the initial cytology was inconclusive.

Related Terms

CDKN2A, BAP1, Mesothelioma, Immunohistochemistry, Pleural Biopsy, Cytology

Notes

• Ask your pathologist or oncologist whether FISH for CDKN2A (9p21) was performed, especially if the diagnosis was based on pleural fluid or a small biopsy where benign versus malignant can be hard to distinguish.
• Request that the pathology report, FISH report, and any images be released to you in full; these documents are important both for second opinions at a mesothelioma specialty center and for any legal claim.
• A negative FISH result doesn't rule out mesothelioma. Roughly 25–30% of mesotheliomas do not show the CDKN2A deletion, so it is interpreted alongside BAP1 staining and standard immunohistochemistry.
• If your hospital does not perform FISH in-house, ask whether the tissue block can be sent to a reference laboratory; preserved tissue blocks remain testable for years.