Sporadic and medullary carcinomas vary in their degree of malignancy. In some the condition is cured by thyroidectomy, while in others, especially in patients who present initially with lymph node metastases, the tumour may metastasise widely within one or two years to mediastinal nodes, lungs, bones, and the liver.
Papillary carcinomas may prove fatal as a result of lymphatic spread to the trachea, with resultant ulceration. More commonly, death occurs in papillary, follicular, and anaplastic carcinomas due to vascular spread to the lungs, brain, liver, and bones. Bone metastases usually involve the vertebrae, pelvis, and ribs; however, they may also occur in the long bones.
