The present invention provides, inter alia, methods for treating, preventing, or ameliorating the effects of a lymphoid malignancy, such as those associated with a mutated phosphatase and tensin homolog (PTEN) gene, or T-cell acute lymphoblastic leukemia (T-ALL). These methods include administering to a subject an effective amount of a phosphoinositide 3-kinase-delta (PI3Kδ) inhibitor and a phosphoinositide 3-kinase-gamma (PI3Kγ) inhibitor. The present invention also provides pharmaceutical compositions for treating the effects of a lymphoid malignancy. This invention further provides a method for identifying a subject who may benefit from co-treatment with a PI3Kδ inhibitor and a PI3Kγ inhibitor. This method includes determining from a sample of the subject whether the subject has a mutated PTEN gene. Additionally, this invention provides methods for identifying a compound that has both PI3Kδ and PI3Kγ inhibitory activity.
