Merck Manual

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Overview of Cancer


Robert Peter Gale

, MD, PhD, DSC(hc), Imperial College London

Last full review/revision Nov 2020
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Cancer is an unregulated proliferation of cells. Its prominent properties are

  • A lack of differentiation of cells

  • Local invasion of adjoining tissue

  • Metastasis, which is spread to distant sites through the bloodstream or the lymphatic system (often)

The immune system Overview of the Immune System The immune system distinguishes self from nonself and eliminates potentially harmful nonself molecules and cells from the body. The immune system also has the capacity to recognize and destroy... read more may play a role in eliminating early cancers or premalignant cells. This concept is termed immune surveillance. Patients with congenital or acquired immunodeficiency have an increased cancer risk, particularly those cancers associated with viral infection, kidney cancer, and melanoma.

Most cancers are potentially curable, particularly if detected at an early stage, and long-term remission is often possible in those detected at later stages. There is controversy whether cancers detected at an early stage, such as breast cancers detected by screening mammography or prostate cancers detected by screening prostate-specific antigen (PSA) testing, will progress during a patient's lifetime. However, for many cancers early detection increases the potential for cure.

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