Mechanisms contributing to susceptibility to tumors in patients with PIDs. ALPS indicates autoimmune lymphoproliferative syndrome; CVID, common variable immunodeficiency diseases; CD40LG, CD40 ligand gene; WAS, Wiskott-Aldrich syndrome; XLA, X-linked agammaglobulinemia; XLN, X-linked neutropenia (allelic to WAS); and XLP, X-linked lymphoproliferative disease.