Telomerase is a ribonucleoprotein that maintains telomeres and is essential for 
cellular immortality and tumour growth. The differential expression of 
telomerase in cancer cells makes it an attractive therapeutic target. Anti-sense 
oligonucleotides directed against the RNA template of hTR and small molecules 
that can interact and stabilise the G-quadruplex represent promising therapeutic 
strategies. Human trials investigating the potential role of the catalytic 
subunit hTERT as a universal cancer vaccine have already commenced. Alternative 
lengthening of telomeres (ALT) and efficacy delay remain important limitations 
to anti-telomerase therapy.