Chemotherapy, the go-to for oncologists. But have you ever wondered how it was discovered? Cancer chemotherapy can be traced back to Germany’s introduction of chemical warfare during World War I. After the war, researchers noticed that mustard gas destroyed bone marrow and lymphatic tissue, and thought it might also be able to kill cancer cells in the lymph nodes. During the war, the chemical weapon mustard gas (sulfur mustard) was found to have antitumor properties. Chemotherapy treatments generally include either chemical, plant, or synthetic ingredients.