Telomerase is a ribonucleoprotein complex that elongates telomeres by adding hexameric (TTAGGG) repeats to the telomeric ends of the chromosomes, thus compensating for the continued erosion of telomeres. Telomerase activity is present in unicellular organisms and germ cells, both places where it is expected to play a role in indefinite cycling and protection from shortening of the telomeres. One phenotypic manifestation that is virtually pathognomonic of several cancer cells is the telomerase activity. Telomerase activity is enhanced in several cell types after treatment with ionizing radiation (IR). Whether there is a direct correlation between the levels of telomerase activity and IR response for tumor cell kill is yet to be addressed in detail. In this review, information is summarized on telomerase activity as a measure for monitoring the radiocurability of tumors. As tumor growth is partly due to deregulated cell cycling, insights into telomerase activity through the cell cycle may prove helpful in designing therapeutic agents either for telomerase activation in cells where its expression can overcome senescence and prolong the life of post-mitotic cells, or inhibition of telomerase where it is essential for proliferation and thus can provide a therapeutic advantage to kill the tumor cells.

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