Cancer drugs are most effective when given in combination. The rationale for combination therapy is to use drugs that work by different mechanisms, thereby decreasing the likelihood that resistant cancer cells will develop. When drugs with different effects are combined, each drug can be used at its optimal dose, without intolerable side effects. (See also Cancer Treatment Principles.)
For some cancers, the best approach is a combination of cancer surgery, radiation therapy, and chemotherapy or other cancer drugs. Surgery or radiation therapy treats cancer that is confined locally, while cancer drugs also kill the cancer cells that have spread to distant sites. Sometimes radiation therapy or drug therapy is given before surgery to shrink a tumor, thereby improving the opportunity for complete surgical removal (this technique is called neoadjuvant therapy). Radiation therapy and/or drug therapy given after surgery (called adjuvant therapy) help to destroy any remaining cancer cells.
The stage and type of the cancer often determines whether single therapy or combination therapy is needed. For example, early-stage breast cancer may be treated with surgery alone or surgery combined with radiation therapy, drug therapy, or with all three treatments, depending on the size of the tumor and the risk of recurrence. Locally advanced breast cancer is usually treated with chemotherapy, radiation therapy, and surgery.
Sometimes combination drug therapy is used not to cure but to reduce symptoms and prolong life. Combination drug therapy can be useful for people with advanced cancers that are not suitable for radiation therapy or surgical treatment (for example, people with non–small cell lung cancer, esophageal cancer, or bladder cancer that cannot be completely removed by surgery).