Moreover, while class IA PI3Kα and β isoforms are widely expressed in endothelial, epithelial and tumor cells, PI3Kδ is expressed in T and B lymphocytes, and the class IB isoform PI3Kγ is expressed in leukocytes and especially in myeloid cells, where it is the major PI3K isoform [46,47,48]. This evidence concerns the gene PIK3CD and neoplasm.