PIK3CD and mantle cell lymphoma: This pathway integrates signals from extracellular stimuli to regulate fundamental cellular processes, including mRNA translation, cell cycle progression and cell survival.[2] MCL tumors frequently express the inactive phosphorylated form of PTEN, a negative PI3K regulator, thereby contributing to constitutive PI3K signaling.[3] In addition, gene amplification of PIK3CA (PI3K p110 catalytic subunit alpha) has also been described in MCL.[4]