Chemotherapy, often referred to as "chemo," uses drugs to kill cancer cells or prevent them from growing. It is a systemic treatment that circulates throughout the body, targeting cancer cells wherever they may be. Chemotherapy is often used when cancer has spread to different parts of the body or when the cancer is known to be responsive to chemotherapy drugs. It can be used as the primary treatment or in combination with other treatments like surgery or radiation therapy. The side effects of chemotherapy can include hair loss, nausea, fatigue, and a weakened immune system.