He is regarded as the father of modern chemotherapy for his work using folic acid antagonists to combat leukemia, which led to the development of other chemotherapeutic agents against other malignancies.

Only basic forms of treatment were available, including red blood cell transfusions and antibiotics, leading to survival rates of merely weeks to months after diagnosis.

Despite general pessimism in the scientific community towards efforts to cure cancer, Farber became dedicated to the battle against childhood leukemia in 1947 during his assistant professorship at Children's Hospital and Harvard Medical School.

Realizing this, he attempted to use a folate antagonist, aminopterin, to block the function of folic acid in patients with leukemia in hopes of achieving remission.

[8] While many practicing physicians responded to these results with enthusiasm, many scientists expressed disbelief and resistance against the new drug since Farber, a young pathologist at the time, was viewed as presumptuous.

However, Farber's discovery marked a breakthrough in cancer research since no drugs had previously been found effective against tumors of the bodily fluids.

[8] While working at Harvard Medical School on a research project funded by a grant from the American Cancer Society, he carried out both the preclinical and clinical evaluation of aminopterin (synthesized by Yellapragada Subbarow).

[10] In 1939, during his appointment at the Children's Hospital, Farber worked with colleague Jerome S. Harris to publish a classic description of the transposition of the great blood vessels in the heart.

Together they created the Children's Cancer Research Foundation (CCRF), which was one of the first nationwide fundraising efforts to take full advantage of modern media, such as a broadcast of the radio show Truth or Consequences.

Despite having Burkitt lymphoma, rather than leukemia, Gustafson (nicknamed 'Jimmy' for publicity purposes) became an inspiration for all pediatric cancer patients and triggered the renaming of the CCRF to the Jimmy Fund.

[4] Beginning in the early 1950s, and continuing until his death in 1973, Farber became a star presenter at Congressional hearings on appropriations for cancer research.