RET and medullary thyroid gland carcinoma: In the present study, we showed that the exposure of RET oncogene mutant-expressing MTC cell lines to an NDI-based G4 ligand resulted in pronounced down-regulation of RET expression at mRNA and protein level, as a consequence of the capability of the NDI derivative to stabilize the G4 structure that spontaneously forms within RET promoter [15, 16].