Thyroid Carcinoma, Anaplastic

**Definition:** An aggressive THYROID GLAND malignancy which generally occurs in IODINE-deficient areas in people with previous thyroid pathology such as GOITER. It is associated with CELL DEDIFFERENTIATION of THYROID CARCINOMA (e.g., FOLLICULAR THYROID CARCINOMA; PAPILLARY THYROID CANCER). Typical initial presentation is a rapidly growing neck mass which upon metastasis is associated with DYSPHAGIA; NECK PAIN; bone pain; DYSPNEA; and NEUROLOGIC DEFICITS.

**Tree numbers:** - C04.557.470.200.725

**Synonyms:** - Thyroid Cancer, Anaplastic