A definitive diagnosis of primary mucinous carcinoma of the thyroid gland is difficult to establish, as some types of papillary carcinomas, follicular carcinomas, medullary carcinomas, and thyroid metastases from cancers of other organs also produce mucin, which is an important feature of primary mucinous carcinomas of the thyroid gland [5–7]. This evidence concerns the gene MUC5AC and thyroid gland papillary carcinoma.