HRAS and KRAS variants account for 20% to 30% of the sporadic MTC cases [7, 8, 15, 18-21] and recently, was reported 3 cases of sporadic MTC devoid of RET and RAS alterations, but instead marked by biallelic inactivation of NF1, leading to loss of heterozygosity (LOH) in a tumor suppressor gene known to activate the Ras pathway signaling [22, 23]. Here, KRAS is linked to medullary thyroid gland carcinoma.