While ATRX has been identified as the most common mutation in ALT cancers, its knockout in SV40 large T antigen (SV40 LT)-transformed primary fibroblasts only increased the frequency of immortalization via ALT by about two-fold over those with wildtype ATRX or DAXX36–38, implying that additional changes are required to induce ALT and immortalize cells. This evidence concerns the gene ATRX and cancer.