How It Spreads Papillary carcinomas spread to nearby lymph nodes and the tissues in the neck, with metastatic lesions to the lungs and bones. With follicular carcinomas, local spread to lymph nodes is less common. These tumors spread through the bloodstream, with metastasis occurring more often to bone. Anaplastic carcinoma usually extensively invades surrounding tissue. Medullary carcinoma spreads to lymph nodes and may invade blood vessels with metastases to the liver.
What Causes It Thyroid cancer is associated with significant excess or deficiency of iodine in the diet, some inherited diseases and especially with exposure to radiation. There is an increased incidence of thyroid cancer among survivors of the atomic blasts in Japan.
The risk of radiation exposure to the neck is now well known, and radiation therapy to treat benign conditions of the head and neck—a common practice in the first half of this century—fortunately has been abandoned. This should eventually lead to a decrease in the incidence of thyroid cancer, but there is a long period between radiation exposure and the development of a tumor.
One new method of preventing thyroid cancer was used on a wide scale with children in the Chernobyl region of Russia after the nuclear reactor accident. Potassium iodide was given to some children in an attempt to block thyroid uptake of radioactive iodine in the fallout. It will probably take at least 30 years to know if this approach was effective. Unfortunately, 200 cases of childhood thyroid cancer have already been diagnosed.
