[18F]FDG-PET measurements have been used in several early-phase clinical trials of PI3K inhibitors in breast cancer (Hanker et al., 2019), and 13C MRS measurements of hyperpolarized [1-13C]pyruvate metabolism detected PI3K inhibition in preclinical studies in glioblastoma (Venkatesh et al., 2012) and breast cancer models (Ward et al., 2010). Here, PIK3CA is linked to glioblastoma.