TERF1 and digestive system neoplasm: In contrast, Karlseder et al. [46] disputed the role of TRF1 in regulating telomere length because they found that complete TRF1 deletion in mice showed no defects in the telomere length or telomere capping.TRF1 is overexpressed in several cancer types, such as renal cell carcinoma [47] and gastrointestinal tumors [48], and is upregulated in glioblastoma multiforme (GBM) [49].