CDKN1A and medullary thyroid gland carcinoma: On univariate logistic regression analysis, CDKN1A SNP showed consistent and significant association with reduced risk of MTC in both hereditary (OR = 0.52; 95% CI = 0.27‐0.99; P = .048) and sporadic MTC groups (OR = 0.63; 95% CI = 0.45‐0.88; P = .007).