PIK3CD is a gene that encodes a protein which is an integral part of the phosphatidylinositol 3-kinase (PI3K) signaling pathway. This pathway is crucial for various cellular functions including cell growth, proliferation, survival, and metabolism. The PIK3CD protein specifically refers to the delta isoform of the catalytic subunit of PI3K. It is predominantly expressed in immune cells and plays a significant role in the regulation of immune responses. Abnormal activation or mutations in the PIK3CD gene can lead to a range of diseases including certain types of leukemia and other immune-related disorders. Understanding its function and regulation is important for developing targeted therapies in cancer and immune system disorders.