Transgenic mice with human NRAS oncogene expression in the thyrocytes under the control of Tg promoter (Tg-NRAS) developed thyroid adenomas (11%) and invasive follicular carcinomas (40%), with approximately 25% showing poor differentiation, lymphovascular invasion and increased metastatic risk [28,30]. This evidence concerns the gene NRAS and thyroid gland follicular carcinoma.