In the study of Barthel et al. [45], 22% of the cases had no detectable TERT expression nor alterations in the genes directly linked to ALT activation—ATRX and DAXX. Barthel et al. [45] hypothesized that not all tumours harbour immortalized cells with a TMM or that additional mechanisms may yet exist, ‘something’ we may designate as a non-defined TMM. Here, ATRX is linked to neoplasm.