A radio-sensitizing pyrimidine nucleoside with potential antineoplastic activity. Cytochlor is metabolized first to a phosphate derivative, CldCMP, by the enzyme deoxycytidine kinase and then to the active uracyl derivative, CldUMP, by the enzyme dCMP deaminase; deoxycytidine kinase and dCMP deaminase have been found in abnormally high concentrations in most cancers. CldUMP, the active metabolite, incorporates into DNA and, upon exposure to radiation, induces the formation of uracil radicals and double-strand DNA breaks. or The study of chromosomes, which are long strands of DNA and protein that contain most of the genetic information in a cell. Cytogenetics involves testing samples of tissue, blood, or bone marrow in a laboratory to look for changes in chromosomes, including broken, missing, or extra chromosomes. Changes in certain chromosomes may be a sign of a genetic disease or condition or some types of cancer. Cytogenetics may be used to help diagnose a disease or condition, plan treatment, or find out how well treatment is working.