GPT and cancer: Thus, considering that telomeric heterochromatin has been reported to stimulate ALT features including high levels of TERRA, that TERRA contributes to the formation of telomeric heterochromatin, that the levels of TERRA are indeed increased in ALT cells relative to telomerase-positive cancer cells, and that TERRA transcripts can form R-loops in telomeric regions, the aforementioned differential effect of trabectedin could be related to the epigenetic status of telomeres [45,46,51,52,53,54,55,56].