Radiopharmaceuticals (Radionuclide Therapy)

A therapeutic radiopharmaceutical typically has three parts: a radioactive atom, a targeting molecule that recognizes and latches onto a feature of cancer cells, and a linker joining the two. After the drug is swallowed or injected, it circulates in the blood and accumulates in the tissue its target defines. As the radioactive atom decays, it releases energy that damages the DNA of the cell it is bound to and roughly 10 to 30 neighboring cells — enough to strike a tumor deposit while limiting harm to more distant healthy tissue. Each agent finds its target differently. Iodine naturally concentrates in thyroid tissue, so I-131 irradiates thyroid cancer cells wherever they are in the body. Radium-223 mimics calcium and builds into areas of intense bone turnover around bone metastases in prostate cancer. Lu-177 dotatate binds somatostatin receptors on neuroendocrine tumor cells; in the trial that led to its 2018 approval, it raised the proportion of patients whose tumors shrank from about 7% to about 17%. Radiopharmaceuticals targeting the PSMA protein in prostate cancer work on the same principle. After some treatments, especially radioactive iodine, the body gives off radiation for a time, so simple precautions around other people are recommended for several days.