[Recent progress in radionuclide therapy]

Therapeutic use of radionuclides includes 131I for thyroid cancer and hyperthyroid Graves' disease, 89SrCl3 for metastatic bone tumors, 131I-MIBG for malignant pheochromocytoma and neuroblastoma, and radioimmunotherapies. 131I is concentrated in 60-70% of metastases from differentiated thyroid cancer following total thyroidectomy. Radioiodine uptake in metastatic lesions is greater in younger patients than in older ones. Hypothyroidism is often mild or even absent in patients with a large amount of tumor tissue, indicating that thyroid hormones produced by highly differentiated tumors compensate partially or even completely for hypothyroidism following total thyroidectomy. Adequate uptake of 131I has been reported to be associated with significant reduction in the size and number of metastases, and with lower recurrence and higher survival rates. Other favorable factors for longer survival are younger age, well-differentiated histological type, small disease extent, and early discovery of metastases. Older patients with extensive metastases and/or bulky tumor masses in the bone have a poor prognosis. Therefore, it is important to discover metastases as early as possible, when patients are still young. Long-term follow-up with periodic thyroglobulin measurements and imaging studies is strongly recommended. In Japan, 131I treatment for Graves' disease is performed only in selected patients in whom antithyroid drugs cannot be used because of side effects or not effective, considering the high prevalence of permanent hypothyroidism. 89SrCl3 is useful for reducing pain due to bone metastases of malignant tumors. 131I-MIBG therapy is effective for improvement of QOL in some patients with metastatic malignant pheochromocytoma. Radioimmuno-therapy using anti-CD20 has been used successfully in clinical application in patients with malignant B cell lymphoma.