RET and thyroid cancer: High-risk history: History of thyroid cancer in one or more first degree relatives; history of external beam radiation as a child; exposure to ionizing radiation in childhood or adolescence; prior hemithyroidectomy with discovery of thyroid cancer, FDG avidity on PET scanning [8]; MEN2/FMTC-associated RET protooncogene mutation, calcitonin >100 pg/mL.