As a cancer treatment, immunotherapy uses the patient’s immune system to help treat their cancer. By producing proteins, cancer often avoids detection from our immune system. When the immune system can't detect the cancer, it cannot fight it. This is how immunotherapy helps. It boosts or restores the patient's immune system, so that it is better able to find and destroythe cancer cells. In this video, medical oncologist Dr. Stephen Lemon explains how immunotherapy works as a cancer treatment, including what types of side effects patients may experience.