Comet Assay

The comet assay (also called single-cell gel electrophoresis) is a laboratory test that measures DNA damage inside individual cells. Damaged DNA fragments migrate out of the cell nucleus during electrophoresis, forming a tail that looks like a comet under the microscope. The longer and brighter the tail, the more DNA breakage has occurred.

Origin

Developed by Östling and Johanson in 1984 and refined into its modern alkaline form by Singh and colleagues in 1988. The name comes from the comet-shaped image produced when fragmented DNA migrates away from the intact nucleus during electrophoresis.

Significance in Asbestos Context

The comet assay is one of the laboratory tools researchers use to show that asbestos fibers physically damage DNA in lung and mesothelial cells, a key step in the chain of causation linking exposure to cancer. Studies using the assay have demonstrated that chrysotile, crocidolite, and amosite all produce measurable DNA strand breaks, supporting the scientific consensus that there is no safe threshold of exposure. In litigation, this kind of mechanistic evidence helps experts explain to juries how even relatively low-level or short-duration exposures can initiate the biological changes that lead to mesothelioma or lung cancer decades later. Defendants sometimes argue that in vitro DNA damage does not translate to human disease, so experts typically pair comet assay findings with epidemiological and pathological evidence.

Example Sentence

The plaintiff's expert cited comet assay studies showing that chrysotile fibers cause DNA strand breaks in human mesothelial cells, rebutting the defense argument that chrysotile is biologically inert.

Related Terms

Genotoxicity, Reactive Oxygen Species, Mechanism of Carcinogenesis, Chrysotile, Mesothelial Cells, Dose-Response

Notes

• If your case involves disputes over whether a specific fiber type (especially chrysotile) can cause mesothelioma, ask your legal team whether their experts intend to cite comet assay or other genotoxicity data.
• Preserve any pathology slides and tissue blocks from your biopsies. They cannot be used for comet assay directly, but they support the parallel fiber-burden and molecular analyses experts rely on.
• When reading expert reports, look for references to 'DNA strand breaks,' 'genotoxicity,' or 'single-cell gel electrophoresis'. These typically signal comet assay evidence being used to establish mechanism.