Cancer chemotherapy and treatment involves several methods. Chemotherapy uses drugs to prevent or treat cancer by killing cancer cells. Common chemotherapies include fluorouracil, capecitabine, and cytarabine which are pyrimidine analogues that interfere with DNA synthesis in cancer cells. These drugs have similar mechanisms of action but different routes of administration and toxicity profiles. Combination chemotherapy uses multiple agents to increase effectiveness while reducing resistance. Careful dosing and administration is needed due to the narrow therapeutic index of chemotherapy drugs.