It was the preferential expression of p110δ in leukocytes (Chantry et al., 1997; Vanhaesebroeck et al., 1997b) together with the absence of somatic mutations in PIK3CD gene that placed p110δ PI3K in the realm of immune system and hematologic cancers. The gene discussed is PIK3CD; the disease is hematopoietic and lymphoid cell neoplasm.