GPT and cancer: Telomeric R-loops are detectable in human primary cells (Shiromoto et al., 2021) and HeLa cells (Feretzaki et al., 2020), while ALT cancer cells and ICF syndrome cells, in which TERRA is transcribed at a higher than normal level (Yehezkel et al., 2008; Arora et al., 2014), appear to have more telomeric R-loops (Arora et al., 2014; Min et al., 2017; Nguyen et al., 2017; Sagie et al., 2017).