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THE MERCK MANUAL MEDICAL LIBRARY: The Merck Manual of Medical Information--Home Edition
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Introduction
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Section

Cancer

Subject

Overview of Cancer

Topics

Introduction· Defenses Against Cancer· Development and Spread· Risk Factors· Types

Introduction

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Pronunciations

metastasis

neoplasm

A cancer is a group of cells (usually derived from a single cell) that has lost its normal control mechanisms and thus has unregulated growth. Cancerous (malignant) cells can develop from any tissue within any organ. As cancerous cells grow and multiply, they form a mass of cancerous tissue—called a tumor—that invades and destroys normal adjacent tissues. The term "tumor" refers to an abnormal growth or mass; tumors can be cancerous or noncancerous. Cancerous cells from the primary (initial) site can spread (metastasize) throughout the body.
Talking About Cancer

  • Aggressiveness:
    The degree to which (or speed at which) a tumor grows and spreads.
  • Anaplasia:
    A lack of differentiation. Thus, an anaplastic cancer is highly undifferentiated and usually very aggressive.
  • Benign:
    Noncancerous.
  • Carcinogen:
    An agent that causes cancer.
  • Carcinoma-in-situ:
    Cancerous cells that are still contained within the tissue where they have started to grow and that have not yet become invasive or spread to other parts of the body.
  • Cure:
    Complete elimination of the cancer with the result that the specific cancer will not grow back.
  • Differentiation:
    The extent to which the cancerous cells resemble normal cells—less resemblance means the cancer is less differentiated and more aggressive.
  • Invasion:
    The capacity of a cancer to infiltrate and destroy surrounding tissue.
  • Malignant:
    Cancerous.
  • Metastasis:
    Cancerous cells that have spread to a completely new location.
  • Neoplasm:
    General term for a tumor, whether cancerous or noncancerous.
  • Recurrence (relapse):
    Cancerous cells return after treatment, either in the primary location or as metastases (spread).
  • Remission:
    Absence of all evidence of a cancer after treatment.
  • Survival rate:
    The percentage of people who survive for a given time period after treatment (for example, the 5-year survival rate is the percentage of people who survive 5 years).
  • Tumor:
    Abnormal growth or mass.

Last full review/revision February 2003
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