Telomeres are the specialized nucleoprotein structures associated with eukaryotic chromosomal ends, which are essential for maintaining the stability of the linear eukaryotic chromosomes. Progressive telomere shortening is an inevitable occurrence in normal somatic cells due to the end-replication problem leading to limited replication efficiency. The hallmark characteristics of human cancer cells include infinite reproductive potential, uncontrolled proliferation and immortality. These abilities of transformed cancerous cells are mainly due to the maintenance of their telomeres since degradation of chromosomal telomeric ends leads to cellular senescence or death. Thus telomere biology is important in the study of human cancer development. The mechanism by virtue the cancer cells are able to divide indefinitely is by maintaining telomeres. Activity of telomerase, a telomere-elongating ribonucleoprotein reverse transcriptase enzyme, is responsible for inducing the property of immortality to cancer cells. In humans nearly about 80% to 90% cancer cells activate telomerase and elongate their telomeres to overcome the end-replication problem. Telomere shortening suppresses cancer formation in contrast according to certain reports it sometimes promotes genomic instability which leads to enhancement of carcinogenesis and consequently the development of malignancy. Majority of cancer cells activate telomerase, but it remains mysterious as to find the reasons of the fact that certain cancer cells often show shorter telomeres in comparison to the cells in the surrounding normal tissues. This controversial role of telomerase associated with certain transformed cells leading to the cancerous state in relation to its role in normal cells is an interesting field to study which points out to the fact of development of cancer cells targeting drugs based on telomerase activities as an alternative weapon in combating against this dreaded human disease. The present review focuses on the activity of telomerase in telomere maintenance in the development of cancerous cells in humans, the use of telomerase as an assay technique for cancer detection as well as the anti-cancer therapeutic approach of targeting the telomerase in the current era of treatment of human cancer.
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