For instance, ALT-positive neuroblastomas are characterized by very long (up to >50kb) and heterogeneous telomeres [22,23], along with the presence of ALT-associated promyelocytic leukemia (PML) nuclear bodies (APBs) and abundant extrachromosomal telomeric repeat (ECTR) DNA that can include T-circles (double-stranded circular DNA) and C-circles (partially double-stranded circles in which the C-rich strand is intact), the levels of which correlate with ALT activity [16,24,25]. This evidence concerns the gene GPT and neuroblastoma.