History will probably not look very kindly on chemotherapy because of its destructive effects on the human body and its ability in many instances to cause cancer as much as treat cancer.
The term 'chemotherapy' is derived from 'chemical therapy.' Several decades ago, scientists in the U.S. began systematically testing the efficacy of known chemicals on cancer cells in the laboratory. Prior research had made it clear that in some cases, harmful chemicals such as mustard gas also had the odd ability to kill cancer cells.
The chief problem with chemotherapy is that it does not discriminate. Chemotherapy is designed to intercept cells in the body during cell division, throw a wrench in the process, and allow the cell to die. Consequently, chemotherapy is the most effective against aggressive cancers where the cancer cells are dividing often. It is not as effective against slow growing cancers for the same reason.
This is why chemotherapy causes hair to fall out, sores to develop in the mouth, and people to have numerous problems along their entire digestive tract: because these are places in the body that have cells which divide often.
In some cases the answer is yes. In several types of Hodgkin's and non-Hodgkin's lymphoma, chemotherapy is delivered with the intent to rid the body of cancer and bring about a cure. This is true for some subtypes of leukemia as well, and to a lesser degree other cancers with solid tumors.
However, not all chemotherapy cures cancer. Some chemotherapy drugs just try to shrink tumor size or 'relieve tumor burden.'
The current trend in cancer research surrounds so-called 'targeted treatments,' i.e. drugs that try to kill cancer cells to the exclusion of other, healthy cells in the body—unlike chemotherapy.