Both chemotherapy and targeted therapy are two effective methods for cancer therapy. The difference is that chemotherapy can also kill the normal cells when eliminating the cancer cells. On the other side, the normals cells can survive the targeted therapy, when the growth of cancer cells was limited.
Chemotherapy drugs effectively target processes that cancer cells need to grow and divide, such as the ability of the cancer cells to replicate their DNA. However, many normal cells, like the cells that line the digestive tract, also need to replicate. In short, though chemotherapy drugs are particularly toxic to cancer cells, they also damage healthy cells. The use of standard chemotherapy therefore produces many, and often severe, side effects. Furthermore, these side effects sometimes prevent patients from being able to take high enough doses to fight the cancer most effectively.
The accumulation of knowledge about the specific differences between normal and cancerous cells has allowed for the development of treatments targeted at cancer-specific activities. One of the most fundamental changes found in cancer cells is the presence of mutations in the genes that are responsible for causing cell growth (oncogenes). The defective proteins produced by these altered genes are prime candidates for targeted therapy. As an example, some cancers are caused in part by mutant proteins that send constant signals into the cell causing cell division. Drugs that block only the mutant form of the protein but do not interfere with the activity of the normal version would only affect cancer cells, and would leave healthy cells untouched.
The specificity of current drugs does have one drawback. Blocking a single pathway in a cancer cell may be enough to slow it down, but it often does not inhibit the cancer enough to kill it. Therefore, many specific cancer drugs are currently being used together with traditional chemotherapy. The combination of a highly specific cancer drug that is able to attack a tumor's weaknesses, and standard chemotherapy to deliver a powerful attack on the tumor, may prove to be an excellent means of treating cancer.