RET and metastatic malignant neoplasm in the lymph nodes: In sporadic MTCs, RET G691S polymorphism allele frequency was found to be higher compared to controls (27.83% vs. 18.86%, p = 0.029) [108,111] and associated with higher preoperative calcitonin levels (p < 0.001) and more frequent lymph node metastases (p < 0.05) compared to patients without RET G691S [117]; however, these data were not confirmed in other studies [112,118,119,120].