TY - CHAP M1 - Book, Section TI - Drug Resistance A1 - Cole, Susan P.C. A1 - Tannock, Ian F. A2 - Tannock, Ian F. A2 - Hill, Richard P. A2 - Bristow, Robert G. A2 - Harrington, Lea PY - 2016 T2 - The Basic Science of Oncology, 5e AB - A major problem with systemic treatment of cancers is the presence or induction of drug resistance in the tumor cells. In practice many types of cancer that occur commonly in humans (eg, colon cancer, most types of non–small cell lung cancer, pancreatic cancer) have a limited response to treatment with current anticancer drugs. Other human tumors (eg, breast cancer, ovarian cancer, or small cell lung cancer) often respond to initial treatment, but acquired resistance to further therapy usually prevents drug treatment from being curative. Resistance to chemotherapy may have multiple causes, and the most widely studied of these are genetically determined mechanisms that lead to resistance of the individual tumor cells. Sensitivity to drugs may differ widely among cell populations from tumors and normal tissues and also among the cells of a single tumor. The selection or induction of a drug resistant subpopulation in human tumors is a major factor limiting the efficacy of clinical chemotherapy. Even if drug-resistant cells are present initially only at low frequency (eg, 1 drug resistant cell per 105 drug-sensitive cells), their selective advantage during drug treatment will lead to their rapid emergence as the dominant cell population, giving the clinical impression of "acquired resistance." SN - PB - McGraw-Hill Education Medical CY - New York, NY Y2 - 2024/04/19 UR - hemonc.mhmedical.com/content.aspx?aid=1127473477 ER -