 Complete the following phrase:  The first use of small-molecule drugs to treat cancer was in the early 20th century, although the specific chemicals first used were not originally intended for that purpose. Mustard gas was used as a chemical warfare agent during World War I and was discovered to be a potent suppressor of hematopoiesis blood production. A similar family of compounds known as nitrogen mustards were studied further during World War II at the Yale School of Medicine. It was reasoned that an agent that damaged the rapidly growing white blood cells might have a similar effect on cancer. Therefore, in December 1942, several people with advanced lymphomas cancers of the lymphatic system and lymph nodes were given the drug by vein, rather than by breathing the irritating gas. Their improvement, although temporary, was remarkable. Concurrently, during a military operation in World War II, following a German 