Merck Manual

Please confirm that you are a health care professional

honeypot link

Overview of Cancer

By

Robert Peter Gale

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

Last full review/revision Sep 2022| Content last modified Sep 2022
Click here for Patient Education

Cancer is an unregulated proliferation of cells. Its prominent properties are

  • A lack of cell differentiation

  • 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.

Many 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.

When cure is not possible, as in many cases of advanced cancer, judicious treatment with surgery Surgery for Cancer Surgery is the oldest effective cancer therapy. It can be used alone or in combination with other modalities (see also Overview of Cancer Therapy). The size, type, and location of the cancer... read more , chemotherapy Chemotherapy Systemic cancer therapy includes chemotherapy (ie, conventional or cytotoxic chemotherapy), hormone therapy, targeted therapy, and immune therapy (see also Overview of Cancer Therapy). The number... read more , immune therapy Immune Therapy Systemic cancer therapy includes chemotherapy (ie, conventional or cytotoxic chemotherapy), hormone therapy, targeted therapy, and immune therapy (see also Overview of Cancer Therapy). The number... read more , and/or radiation therapy Radiation Therapy for Cancer Radiation therapy can cure many cancers (see also Overview of Cancer Therapy), particularly those that are localized or that can be completely encompassed within a radiation field. Radiation... read more may improve quality of life and prolong survival. However, in other patients, particularly in patients with poor functional status and in those with comorbid conditions, such treatment may be poorly tolerated, and palliative care Palliative Care and Hospice Dying patients can have needs that differ from those of other patients. So that their needs can be met, dying patients must first be identified. Before death, patients tend to follow 1 of 3... read more may be appropriate.

Click here for Patient Education
NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
quiz link

Test your knowledge

Take a Quiz! 
iOS ANDROID
iOS ANDROID
iOS ANDROID
TOP