PD-L1 is a protein called programmed death-ligand 1, which is on many cells, including some cancer cells. It binds to the PD-1 protein receptor on a type of immune cell called a T cell. When bound, PD-1 and PD-L1 regulate the normal immune response by blocking the T cells from killing other healthy cells. These are called checkpoint proteins as they function to keep the immune system in check. When PD-L1 protein activity is inhibited, the T cells can be harnessed to attack and kill cancer cells. PD-L1 inhibitors are a category of immunotherapy drugs called checkpoint inhibitors that suppresses the immune mechanism and instead increase the ability of T cells to kill cancer cells.

Currently there are three PD-L1 inhibitors used in immunotherapy treatments: Atezolizumab, avelumab, and durvalumab. Clinical indications for these drugs include:

  • Lung cancer
  • Bladder cancer
  • Merkel cell carcinoma (a type of skin cancer)

Because these drugs activate the immune system, it is possible some healthy tissues are affected by the activated immune system during treatment and lead to some unique potential treatment-related adverse events, sometimes referred to as irTEAEs (immune-related, treatment-emergent adverse events). This can lead to problems in the lungs, intestines, liver, kidneys, hormone-making glands, and other organs may occur. These irTEAEs are quite different from the typical side effects of chemotherapy and have been well-characterized. They include:

  • Fatigue (due to hypophysitis)
  • Cough or shortness of breath (due to pneumonitis)
  • Nausea, abdominal pain, diarrhea (due to colitis)
  • Joint pain (arthritis)
  • Skin rash (dermatitis)