Early studies of the in vitro effects demonstrated RET inhibition and death of oncogene-addicted MTC cells [14, 33], but these studies demonstrated successful RET inhibition only at serum concentrations that could not be achieved with tolerable doses of imatinib, and subsequent clinical trials of imatinib monotherapy revealed no responses in MTC [32, 34]. Here, RET is linked to medullary thyroid gland carcinoma.