Several experimental studies suggest that resistance to chemotherapy of MTC may be circumvented by modulating the expression of MDR1 and/or MDR2, focusing the attention of researchers on MDRs as novel therapeutic targets (Massart et al. 1996; Ratnasinghe et al. 2001; Fagin, 2004; Sorokin, 2004; Zatelli et al. 2005; Pérez-Tomás, 2006; Ruggeri et al. 2006). This evidence concerns the gene ABCB4 and medullary thyroid gland carcinoma.