The anaplastic thyroid carcinoma (undifferentiated carcinoma) usually has diverse morphology, obvious cell atypia, easy to see mitotic images, immunohistochemical PAX8 positive (36–76%), but this case has obvious clear cells, mitotic images are rare, PAX8 Negative, but GATA3 positive, which further proves that the tumor originates from the parathyroid gland. Here, PAX8 is linked to undifferentiated carcinoma.