PIK3CD and cancer: Class I PI3Ks, linked with several cancers, comprise a catalytic subunit and a regulatory subunit, further divided into Class IA (p110α, p110β, or p110δ with regulatory subunits p85α, p55α, p50α, p85β, or p55γ) and Class IB (p110γ with regulatory subunits p84 or p101)22.