that have not yet metastasized to distant sites, surgery is often curative, particularly for tumors that are completely localized.

Radiation is the primary treatment for some cancers (e.g., Hodgkin's disease and other lymphomas), but more often, it is used in conjunction with surgery. As an adjuvant to surgery, it is used to destroy remaining cancer cells in and around the site of the primary cancer. It is particularly important, for instance, as an adjunct to lumpectomy for women with early-stage breast cancer and has been demonstrated definitively in randomized trials to reduce the likelihood of a local recurrence. In some cases, radiation is used to shrink the size of a tumor before surgery or in late stages of disease to offer symptom relief by shrinking growths that interfere with eating, breathing, or other functions.

Chemotherapy (including hormone therapy) may be used alone to treat some cancers (e.g., some lymphomas and leukemias), but it is more often used in combination with radiation and surgery. If cancer is found at diagnosis to have spread from its original site (i.e., metastasized), the only potentially curative treatment option is chemotherapy, which can reach cancerous cells around the body. In most cases, patients begin an extended course of chemotherapy, which may last months, after surgery. Like radiation, it may also be used as "neoadjuvant therapy," given before a tumor is surgically removed, with the intent of shrinking the tumor.

With most forms of cancer, higher doses of chemotherapy and radiation are more effective, but they also cause more damage to healthy tissue. The bone marrow (from which most elements of the blood are continuously formed) is particularly sensitive to chemotherapeutic agents and radiation, and doses high enough to control cancer can easily wipe out the bone marrow, killing the patient as well. Over the past decade, oncologists have increasingly used a controversial strategy that employs high-dose chemotherapy and/or radiation treatment in conjunction with autologous bone marrow transplantation, in which patients have some bone marrow removed and stored before they are treated. After treatment, the stored bone marrow cells are reinfused into the patient to repopulate the bone marrow and begin producing blood cells. Bone marrow transplantation using marrow from healthy donors ("allogeneic transplantation") is established as a primary treatment for some leukemias and lymphomas—diseases in which the cancer has arisen in the blood elements themselves—but autologous transplantation still remains of unknown value for the treatment of solid tumors.

Other types of treatment use the body's own immune system to resist disease or invasions. Agents known as biologic response modifiers, which are derived from or modeled on the body's own natural products (e.g., interferon, the interleukins, tumor necrosis factor) are being used in cancer treatment, generally in combination with other treatments.

For most cancers, the majority of physicians and researchers have agreed on one or more "standard treatment approaches"—usually based on research findings, a consensus of expert opinion, or both. Doctors may have different opinions about how to treat some cancers because definitive evidence on what treatment works best (if there are any effective treatments) is not available.

In a few cases, treatments that appear to be of equal effectiveness, but have different implications for quality of life, are available (e.g., watchful waiting versus surgery for some prostate cancers). In these situations, patient preferences often determine the choice of treatment. Patient-centered care is care that incorporates respect for patients' values and preferences, provides information in clear and understandable terms, promotes autonomy in decision making, and attends to the need for physical comfort and emotional support.

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