BTK and cancer: PI3K/ATK/mTOR and Ras/MAPK pathway activation are involved with constitutive PD-L1 regulation in many cancers; loss of PTEN [23] or mutations in PIK3CA [24] lead to PI3K/ATK/mTOR pathway activation, while mutations in EGFR or Ras [25, 26] lead to Ras/MAPK pathway activation.