<prompt> Which enzymatic mutation is responsible for immortality of cancer cells?DNA reverse transcriptaseRNA polymeraseTelomeraseDNA polymerase  <response>: With respect to cancer, when tumor cells divide rapidly their telomeres often shorten.Such telomeres usually detected in leukocytes because of ease of obtaining them have been implicated as a risk factor for many, but not all, solid tumors eg, breast cancer. Short telomeres appear to be of predictive value regarding the progression of chronic inflammatory diseases such as ulcerative colitis and Barrett esophagus to cancer.The activity of telomerase, the main enzyme involved in synthesizing telomeres, is frequently elevated in cancer cells, providing one mechanism for overcoming telomere shortening. Selective inhibitors of telomerase have been considered as possible drugs for treating cancer, but have not as yet been translated into successful clinical usuage.Key Concept:Telomerase is the main enzyme that is seen elevated in cancer cells.Ref : Harpers illustrated biochemistry, 31st edition. 