The safety and clinical activity of an oral PI3K-β inhibitor, GSK2636771, in combination with paclitaxel for patients with PTEN-deficient advanced-stage GC/GEC (as documented by alterations in the PI3K pathway genes, e.g., PI3KCB, PI3KR1, PTEN, etc., in fresh or archival tumor tissue) is being evaluated in a phase Ib/IIa dose-escalation trial. Here, PTEN is linked to neoplasm.