Answers: Are you asking about chemotherapy? Different chemo drugs work within different ways. Some kill cell that replicate rapidly: because compared to most conventional cells, cancer cell replicate rapidly. Some chemo drugs choke sour the blood supply to tumors. Some targeted drugs bind to tumor cells to prevent them from replicating. There are probably more ways they work than that ... did you look on Wikipedia beneath "chemotherapy"?
I agree with the previous respondent that different chemo drugs work differently. The hollow majority of older agents (still within widespread use) deed against DNA. There are a variety of different ways they achievement, but the end result is that the cancer cell recognize that its DNA is abnormal and destroys itself. These drugs work against any hastily dividing cells (the conception being that DNA is more actively within use in a hurriedly dividing cell). This makes sense when you consider that cancer, by definition, is a disease of hurriedly dividing cells. Unfortunately, your body have lots of normal cell that divide rapidly, too, similar to hair, the cell lining your gut, and blood cell. This explains side effects like pelt loss, mouth sores, and low blood counts, because even these good cell are destroyed by the chemo.
Newer chemo drugs may be targeted against a specific type of tumor and so, theoretically, is smaller quantity toxic to the body's normal cell. The problem is that every type of tumor is so different, and it's nearly impossible to come up with a tricks bullet for each one. Researchers are working concrete in that direction, though.
check out this research group they hold a message board you can use http://boinc.bakerlab.org/rosetta/