GPT and cancer: In germ cells and the vast majority of cancer cells, the shelterin complex also contributes to regulating telomere lengthening, either via telomerase-mediated DNA synthesis (active in 85 – 90% of cancers) or recombination-based alternative lengthening of telomeres (ALT; active in 10 – 15% of cancers) (Cesare and Reddel, 2010).