RET and medullary thyroid gland carcinoma: Medullary thyroid carcinoma accounts for 5-10 % of thyroid malignancies, originates from parafollicular C-cells, is associated with a mutation of the RET proto-oncogene and can be sporadic or familial (25 % of medullary thyroid carcinomas) (Leboulleux et al., 2004[33]).