Telomerase therapeutics for cancer: challenges and new directions.

It has been approximately a decade since telomerase was described as an almost universal marker for human cancer. Most human tumours not only express telomerase but also have very short telomeres, whereas telomerase activity is either reduced or absent in normal tissues, making the inhibition of telomerase an attractive target for cancer therapeutics. Here we review the current status of telomerase therapeutics and discuss future opportunities and challenges for telomerase research, including a possible relationship with cancer stem cells that could be a source of chemo-/radioresistance development in many advanced cancers.