Day One Biopharmaceuticals said Sunday that a targeted therapy shrank tumors by at least 50% in a majority of children with the most common form of pediatric brain cancer, setting up a potential approval in a rare disease long overlooked by drugmakers. The new data expand on earlier results released last year from 22 patients. Of the 69 pediatric low-grade glioma patients now evaluated, 44, or 64%, saw their tumors dwindle to less than half their original size, including three patients whose tumors disappeared.