This is the first peer-reviewed report of an allosteric, mutant-selective PI3Kα inhibitor, STX-478, that reduces PIK3CA-mutant tumor growth in mice. However, in contrast to the FDA-approved PI3Kα isoform-selective inhibitor alpelisib, STX-478 does not induce hyperglycemia or other metabolic dysfunctions. See related article by Buckbinder et al., p. 2432 (7).