What is biological therapy?Biological therapy is a type of treatment that works with your immune system. It can help fight cancer or help control side effects (how your body reacts to the drugs you are taking) from other cancer treatments like chemotherapy. What is the difference between biological therapy and chemotherapy ?Biological therapy and chemotherapy are both treatments that fight cancer. While they may seem alike, they work in different ways. Biological therapy helps your immune system fight cancer. Chemotherapy attacks the cancer cells directly.