Cancer Progress Report 2016: Contents
In this section you will learn:
Cancer is not one disease; it is a collection of diseases characterized by the uncontrolled growth of cells.
Many cancers are progressive in nature, providing distinct points for medical intervention to prevent cancer, detect it early, or treat progressive disease.
The most advanced stage of cancer, metastatic disease, accounts for most cancer-related deaths.
Changes in the genetic material in a normal cell underpin cancer initiation and development in most cases.
A cancer cell’s surroundings influence disease development and progression.
The more we know about the interplay among the individual factors influencing cancer biology, the more precisely we can prevent and treat cancer.
Research has taught us that cancer is a complex disease. In fact, it is not just one disease but rather a collection of many diseases that arise when the processes that control the multiplication and life span of normal cells go awry.
In adults, cell multiplication is a very tightly controlled process that occurs primarily only to replace cells that die due to exposure to various external factors or as a result of normal wear and tear.
If the processes that control the multiplication and life span of normal cells go awry, the cells start multiplying uncontrollably, fail to die when they should, and begin to accumulate. In body organs and tissues, the accumulating cells form a tumor mass, whereas in the blood or bone marrow, they crowd out the normal cells. Over time, some cancer cells within the tumor mass gain the ability to invade local tissues. Some also gain the ability to spread (or metastasize) to distant sites.
The progressive nature of cancer provides distinct sites for medical intervention to prevent cancer, detect it early, or treat progressive disease. In general, the further a cancer has progressed, the harder it is to stop the chain of events that leads to the emergence of metastatic disease, which is the cause of most deaths from solid tumors.
Changes, or mutations, in the genetic material of a normal cell are the primary cause of cancer initiation. Over time, additional mutations are acquired by cells within a growing tumor mass, and this drives cancer progression. The number of cells within a growing tumor that carry a given mutation depends on when the mutation was acquired during tumor growth. Thus, even within the same tumor, different cancer cells may have different genetic changes. In general, the more genetically heterogeneous a tumor is, the harder it is to effectively treat.
Not all mutations acquired by a cell contribute to cancer initiation and development. In fact, the identity, order, and speed at which a cell acquires genetic mutations determine whether a given cancer will develop and, if a cancer does develop, the length of time it takes to happen. Numerous interrelated factors influence mutation acquisition and determine the overall risk that a person will develop a particular type of cancer (see sidebar on
Why Did I Get This Cancer?).
Cancer Development: Influences Inside the Cell
The accumulation of mutations in the genetic material of a cell over time is the predominant cause of cancer initiation and progression (see sidebar on
Genetic and Epigenetic Control of Cell Function). A genetic mutation is a change in the type or order of the four deoxyribonucleic acid (DNA) units, called bases, that make up the genetic material of a cell. The order, or sequence, of DNA bases is a key determinant of what proteins are produced by a cell and how much of each protein is produced. Many different types of mutation contribute to cancer initiation and development, primarily by altering the amount or function of certain proteins (see sidebar on
In addition to genetic mutations, most cancer cells also have profound epigenetic abnormalities, compared with normal cells of the same tissue. In many cases, epigenetic alterations and genetic mutations work together to promote cancer development. Although genetic mutations are permanent, some epigenetic abnormalities appear to be reversible, and harnessing this discovery for therapeutic purposes is an area of intensive investigation.
Cancer Development: Influences Outside the Cell
Genetic mutations that disrupt the orderly processes controlling the multiplication and life span of normal cells are the main cause of cancer initiation and development. However, interactions between cancer cells and their environment—known as the tumor microenvironment— as well as interactions with systemic factors, also have an important role in cancer development (see sidebar on
Cancer Growth: Local and Global Influences). In fact, cancer cells often exploit tumor microenvironment components to promote their multiplication and survival.
Cancer Development: A Whole-Patient Picture
Research has powered an explosion in our understanding of the individual factors inside and outside a cell that cause cancer initiation, development, and progression. It is also beginning to provide us with a picture of how these factors work together and are influenced by each person’s unique biological characteristics. This knowledge is the essence of precision medicine, as well as the more nascent strategy of precision prevention (see
Precision prevention and medicine aim to tailor each person’s health care to the prevention and/or treatment strategies most likely to be of benefit, sparing each person the cost of and potential harms from those prevention interventions and/or treatments that are unlikely to be of benefit (25, 26). As we develop an even more comprehensive, whole-patient understanding of the way in which cancer starts, progresses, and results in sickness, we can expect to see an acceleration in the pace of progress in precision medicine and prevention for cancer (see
Anticipating Future Progress).
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Progress Report 2016 Contents