PIK3CD and breast cancer: Class II PI3Ks comprise the C2α, C2β, and C2γ catalytic isoforms and lack regulatory subunits; thus, they can be activated as monomers.17 In mammals, three class II PI3K isoforms have been identified, among which PI3KC2α and PI3KC2β are broadly expressed, while PI3KC2γ is mainly expressed in the liver.18 PI3KC2α plays a pivotal role in breast cancer progression by affecting mitotic spindle formation.19 In addition, class II PI3Ks contain additional protein-binding domains and an extended N-terminal region, which contributes to intracellular localization.