Cancer Progress Report 2014: Contents
In this section you will learn:
Changes in the genetic material in a normal cell underpin cancer initiation and development in most cases.
A cancer cell’s surroundings influence the development and progression of disease.
The most advanced stage of cancer, metastatic disease, accounts for more than 90 percent of cancer deaths.
The more we know about the biology of cancer, the more precisely we can prevent, detect, diagnose, and treat it.
Cancer arises when the orderly processes that control the multiplication and life span of normal cells go awry. As a result, the cells start multiplying uncontrollably, fail to die when they should, and accumulate, either forming a tumor mass in any organ or tissue of the body or crowding out the normal cells in the blood or bone marrow. Over time, tumors can enlarge as more cells accumulate, until some cells gain the ability to invade local tissues and spread, or metastasize, to distant sites (see
Figure 3). The emergence of metastatic cancer is a dire occurrence that accounts for more than 90 percent of cancer deaths.
The changes in cell behavior that occur during the initiation, development, and progression of a cancer are predominantly a result of changes in the genetic material of the cells. The length of time it takes for a cancer to develop varies widely and depends on the identity, order, and speed at which changes in the genetic material accumulate. Numerous interrelated factors, such as a person’s genetic makeup and environmental factors like tobacco use, diet, associated illnesses, and other exposures, also influence this rate.
Cancer Development: Influences Inside the Cell
The entirety of a person’s deoxyribonucleic acid (DNA) is called their genome (see sidebar on
Genetic and Epigenetic Control of Cell Function). A “mutation” is a change in the type or order of the bases that make up the DNA code. Because a cell reads the DNA code to produce the proteins it needs to function, mutations in the code can result in altered protein amounts or functions (see sidebar on
Genetic Mutations). If these changes alter proteins that control certain critical cell functions, such as cell multiplication or survival, they can ultimately lead to cancer.
Many different types of mutations can lead to cancer. Over the years, researchers have determined that cancer-associated mutations are most often found in one of two classes of genes: (proto)oncogenes and tumor suppressor genes.
Mutations in (proto)oncogenes lead to altered proteins that can drive the initiation and progression of cancer. Tumor suppressor genes code for proteins that normally repair damaged DNA or repress signals that promote cell survival and multiplication. Alterations in these genes can lead to cancer by permitting the accumulation of harmful DNA mutations or allowing overactive cells to survive or begin growing again.
In addition to mutations in their DNA, most cancer cells also have profound abnormalities in their epigenomes when compared with normal cells of the same tissue. In many cases, these epigenetic defects work in conjunction with permanent changes in the DNA of the cell to promote cancerous behaviors. One of the most exciting recent discoveries is that some epigenetic abnormalities may be reversible.
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Cancer Development: Influences Outside the Cell
It is clear that cancer develops as a result of alterations to the genetic material of a cell that lead to malfunctions in its behavior. Research has revealed, however, that interactions between cancer cells and their environment—known as the tumor microenvironment—as well as interactions with systemic factors, are an important part of cancer development (see sidebar on
Cancer Growth: Local and Global Influences). This means that cancer is much more complex than an isolated mass of proliferating cancer cells. Therefore, if we are to advance our mission to prevent and cure all cancers, we must develop a more comprehensive, whole-patient understanding of cancer.
Some components of the tumor microenvironment are normal parts of the tissue in which the cancer is growing. Others are systemic factors that transiently affect the tumor microenvironment as they percolate through it. Yet others are actively recruited or formed as a result of signals emanating from the cancer cells themselves. Whether passive participants or active recruits, the various components of the microenvironment are often exploited by cancer cells to advance their growth and survival.
Cancer Development: Exploiting Our Expanding Knowledge to Improve Health Care
Fundamental research expands our knowledge of the biology of cancer (see sidebar on
Fundamental Research: The Foundation of Today’s Treatments and Tomorrow’s Advances). As our knowledge has grown, so has our ability to exploit it to develop new and improved approaches to cancer prevention, detection, diagnosis, and treatment. The majority of the new approaches more precisely attack cancers than do traditional therapies, providing patients with not just longer but also higher quality lives.
It is clear that through this fundamental research, which is largely supported by the NIH and NCI, we have developed a greater understanding of the processes by which cancer starts, progresses, and results in disease. This knowledge has yielded significant progress in preventing, detecting, diagnosing, and treating cancer. Continued progress, therefore, will be made only through additional research, and as such, it is imperative that the administration and Congress support the primary federal agencies that support this vital research, the NIH and NCI.
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Progress Report 2014 Contents