RET and medullary thyroid gland carcinoma: In fact, one study reported that among 729 patients who appeared to have sporadic MTC and who were studied over a 10-year period, RET genetic screening identified an unsuspected germline RET mutation in 6.5% of these patients (47 out of 729 patients) (24), which would generally reclassify these patients as having FMTC.