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The goal of cancer treatment is first to eradicate the cancer. If this primary goal cannot be accomplished, the goal of cancer treatment shifts to palliation, the amelioration of symptoms, and preservation of quality of life while striving to extend life. The dictum primum non nocere may not always be the guiding principle of cancer therapy. When cure of cancer is possible, cancer treatments may be undertaken despite the certainty of severe and perhaps life-threatening toxicities. Every cancer treatment has the potential to cause harm, and treatment may be given that produces toxicity with no benefit. The therapeutic index of many interventions is quite narrow, and most treatments are given to the point of toxicity. Conversely, when the clinical goal is palliation, careful attention to minimizing the toxicity of potentially toxic treatments becomes a significant goal. Irrespective of the clinical scenario, the guiding principle of cancer treatment should be primum succerrere, "first hasten to help." Radical surgical procedures, large-field hyperfractionated radiation therapy, high-dose chemotherapy, and maximum tolerable doses of cytokines such as interleukin (IL) 2 are all used in certain settings where 100% of the patients will experience toxicity and side effects from the intervention and only a fraction of the patients will experience benefit. One of the challenges of cancer treatment is to use the various treatment modalities alone and together in a fashion that maximizes the chances for patient benefit.
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Cancer treatments are divided into four main types: surgery, radiation therapy (including photodynamic therapy), chemotherapy (including hormonal therapy and molecularly targeted therapy), and biologic therapy (including immunotherapy and gene therapy). The modalities are often used in combination, and agents in one category can act by several mechanisms. For example, cancer chemotherapy agents can induce differentiation, and antibodies (a form of immunotherapy) can be used to deliver radiation therapy. Surgery and radiation therapy are considered local treatments, though their effects can influence the behavior of tumor at remote sites. Chemotherapy and biologic therapy are usually systemic treatments. Oncology, the study of tumors, including treatment approaches, is a multidisciplinary effort with surgical-, radiotherapy-, and internal medicine–related areas of expertise. Treatments for patients with hematologic malignancies are often shared by hematologists and medical oncologists.
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In many ways, cancer mimics an organ attempting to regulate its own growth. However, cancers have not set an appropriate limit on how much growth should be permitted. Normal organs and cancers share the properties of having (1) a population of cells in cycle and actively renewing and (2) a population of cells not in cycle. In cancers, cells that are not dividing are heterogeneous; some have sustained too much genetic damage to replicate but have defects in their death pathways that permit their survival, some are starving for nutrients and oxygen, and some are out of cycle but poised to be recruited back into cycle and expand if needed (i.e., reversibly growth-arrested). Severely damaged and starving cells are unlikely ...