Radiopharmaceutical developers are running into safety issues as more targeted agents move deeper into clinical trials. A STAT+ report describes how radioactive isotopes—though engineered to home in on tumors—can still cause off-target exposure to organs including kidneys, liver, and bone marrow. The story notes the industry’s longstanding rationale: replace broad “whole-body” radiation with pharmacologic delivery of radionuclides that concentrate in malignant tissue. But as candidates enter trials, companies are discovering that targeting is not absolute, and dose-limiting toxicities can arise from unintended biodistribution. With radiopharmaceuticals expanding across oncology programs, the article underscores that safety monitoring and therapeutic index optimization are becoming as central as targeting chemistry and isotope selection.