GPT and neoplasm: To test whether spontaneous telomeric DDR activation in ALT cells8 leads to telomeric dilncRNA accumulation, we compared telomeric dilncRNA levels between the ALT tumor cell lines U2OS, SAOS2 and G292, the non-tumor cell line BJhTERT and the telomerase-positive tumor cell line HeLa – the status of all ALT cell lines was confirmed by elevated C-circle levels (Supplementary Fig. 1a).