The complexity of the PI3K/AKT/mTOR signaling network involves numerous feedback loops, extensive crosstalk nodes with other signaling pathways and compensatory pathways, providing ample opportunities for circumventing the effects of PI3K inhibition. Oncogenic activation of the PI3K pathway promotes cell growth, survival, and resistance to both chemotherapy and radiotherapy. Critically, PI3K pathway activation often occurs alongside pro-tumorigenic aberrations in other signaling networks, thereby enabling a tumor cell to resist the effects of PI3K inhibition and/or to readily develop such resistance.