Clinical and Genetic Studies in Familial Non-medullary Thyroid Cancer

Background: \- Researchers are studying types of thyroid cancer that seem to cluster in families. Non-medullary thyroid cancer accounts for the vast majority of all types of thyroid cancer, but little is known about possible genes that may cause the cancer. More research is needed to develop the best ways to screen for familial non-medullary thyroid cancer (FNMTC) so that it can be diagnosed and treated at an early stage. Objectives: * To evaluate the natural history of FNMTC. * To determine the best screening strategy for FNMTC. * To identify genes that may indicate susceptibility to FNMTC. Eligibility: \- Individuals at least 7 years of age who have two first-degree relatives (e.g., parents, children, siblings) who have or have had non-medullary thyroid cancer or a documented diagnosis of non-medullary thyroid cancer and one living relative with documented non-medullary thyroid cancer. Design: * Participants will be evaluated by family history pedigree, physical examination, imaging (including possible neck ultrasound and radioactive iodine scans), and laboratory testing. * Participants who agree to have blood or other biological samples collected will be asked to enroll in an additional study to provide the appropriate samples and tissues. * After the initial study evaluation, participants who are not found to have a malignant thyroid tumor will be re-screened every year with non-invasive imaging studies. Participants who are found to have a malignant thyroid tumor will be informed of possible treatment options.