Zhang et al. discovered that PTEN-targeting miRNAs, previously determined to be encoded by the miR-17-92 allele [101,102,103,104], are excreted from brain astrocytes in exosomes, thereby mediating an intercellular silencing of PTEN and concomitant activation of PI3K/AKT in metastatic melanoma cells. The gene discussed is PIK3CA; the disease is melanoma.