If a person has multiple nodules, the chance that any of them are cancer is even less. Because thyroid cancer occurs within thyroid nodules, checking nodules for cancer is common. However, a few rare but dangerous kinds of thyroid cancer, or a very advanced thyroid cancer, can still be fatal. The causes of benign thyroid neoplasms and thyroid cancer are complex. Perhaps the best studied cause is ionizing radiation.
Radiation can also cause neoplasms or nodules.
X-rays and gamma radiation have clearly been shown to increase the risk, or chance, that a person might develop a thyroid nodule, either benign or malignant. This information has been gathered from studies of groups or populations of persons who were exposed to gamma radiation or x-rays. Most of these ill-fated treatments were discontinued in the 1960's. In addition, several populations who were exposed to a mixture of external and internal radiation from environmental sources have been studied. Children and adults in the Marshall Islands who were exposed to radioactive fallout from nuclear weapons testing also developed high levels of thyroid nodules from radiation exposure.