Third Myron Karon Memorial Lecture. Resistance of human tumors to cancer chemotherapeutic agents: an important research problem.

The mechanisms whereby malignant cells become biochemically resistant to anti-cancer drugs are surveyed, with emphasis on human tumors. Methotrexate is used as a model to illustrate the mechanisms of resistance that can occur, and how cells can increase their production of dihyrofolate reductase, the target enzyme. Drug resistance remains one of the major impediments to the successful use of chemotherapy for neoplastic diseases.