Chemo developed during World War II, the naval person naval personnel who were exposed to mustard gas during military action were found to have toxic changes in the bone marrow cells that develop into blood cells. At a similar period of time, the U.S. Army were studying a series of chemicals similar to mustard gas to create potent agents for war. During this study of these chemicals, they discovered  a compound called nitrogen mustard in which can compete against cancer.

 

  Shortly after this discovery, Sidney Farber of Boston analyzed that aminopterin blocked a critical chemical reaction needed for DNA duplication.That drug was an antecedent  of methotrexate, which is a drug frequently used today.   

 

   At the beginning of the 20th century, only cancers that were small and could be localized, were able to be removed by surgery and were curable. It was later discovered that the fusion of many chemotherapy drugs had a better effect in destroying the cancer completely than it did in the beginning of the 20th century. [Citation 35]