Chemotherapy can cure certain forms of cancer. Some of these patients have been in remission longer than five years and may, in fact, be cured. Multiple carcinomas of the superficial layers of the skin have been eradicated after the application of certain cancer-drug ointments to the skin. Wilms' tumor, for example, is often curable when cancer drugs are used in combination with surgery and radiation. Many other forms of cancer benefit temporarily or partially by chemotherapy.
Some cancers are resistant to drugs, however.
Most cancer drugs are limited in their usefulness. One problem is that only a certain proportion of cells is dividing at any one time, and most cancer drugs can destroy only that part of the cell population undergoing division. Another problem is that cancer drugs damage normal, as well as cancer, cells and tissues. In addition, some cancer cells eventually become resistant to drugs. To help overcome these difficulties, combinations of chemotherapeutic agents that act on cells in different ways have been used in various treatment programs simultaneously or in sequence.