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Is cancer caused by old age?

The comet assay is a well defined tool for measuring the degradation of DNA.   The principle of the comet assay is based upon the ability of denatured or cleaved DNA fragments to migrate out of the cell under the influence of an electric field, whereas undamaged DNA migrates more slowly and remains within the confines of the cell.


…the risk of cancer increases dramatically with age….

Here the comet assay is used to study the degradation of DNA in the elderly:  the onset of age-related genome instabilities remains a poorly defined subject.  Human genome instability and changes in chromosome morphology are components of two related processes: ageing and the development of malignancies, such as cancer.  We understand that the risk of cancer increases dramatically with age, however chromosome abnormalities and genome instabilities in the elderly does not necessarily indicate cancer occurrence.  Here, 31 generally healthy elderly subjects recruited from the same residential area (16 females and 15 males, aged between 65 and 76) had a blood sample taken.  The results generated from the elderly were compared to those from 31 control subjects (selected from the same residential area, aged between 35 and 47).  Fluorescence in situ hybridization (FISH) chromosome painting probes and a modified comet assay were used to record structural chromosome aberrations and translocations in blood cells. 

…the comet assay revealed a significantly increased
percentage of DNA in the comet tails…

This study used the Comet Assay IV analysis system and for each subject, 100 comets were measured on two parallel slides, recording comet tail length and percentage of DNA in comet tail.  Results of the comet assay revealed a significantly increased percentage of DNA in the comet tails in cells of elderly individuals, while tail lengths did not differ.  The comet assay result was comparable to cells treated with hydrogen peroxide, which was added as a control measure to cause oxidative damage to the cells. The results obtained in this study may indicate that accumulation of genome damage observed in the cells of elderly subjects is directly linked with the ageing process.  However, the accumulation of genome damage might not trigger the mechanism that induces cancer development.

Case Study based on:
Genomic instability in a healthy elderly population: a pilot study of possible cytogenetic markers related to ageing.
Mladinic M, Kopjar N, Milic M, Dasovic AB, Huzak M, Zeljezic D. Mutagenesis. 2010 Sep;25(5):455-62. Epub 2010 May 26.  Division for Mutagenesis, Institute for Medical Research and Occupational Health, Ksaverska 2, 10000 Zagreb, Croatia.