Genetic heterogeneity of BRAF was studied by comparing the mutation status in different samples of tumor as follows: (a) 2 separate areas (each >1.5 cm in diameter) within the primary tumor, (b) a more than 1.5 cm area of primary carcinoma and a second 5 mm area simulating a fine needle aspiration sample from a different portion of the primary tumor, (c) primary carcinoma and its lymph node metastasis at thyroidectomy, (d) primary carcinoma and the recurrent metastasis, and (e) differentiated and anaplastic areas in the primary carcinoma.