We measure progress against cancer in terms of:
* The growth of knowledge about cancer, and
* The reduction of the cancer burden.
Twenty-five years ago three theories of cancer (one based on viral causes, one based on heredity, and a third based on chemical causes) dominated cancer research, but there was little direct evidence to relate these theories to the genesis of the vast majority of human cancers.
Today we know that cancer is a group of diseases that results from a series of changes in genes that control cell growth and behavior. These genetic changes transform a healthy cell into a cancer cell. One of the critical questions in cancer research is how and why these genetic errors occur, and just as important, why the errors are not corrected by the cell's normally efficient surveillance mechanisms. The relationship of these genetic changes to the environment and to behaviors such as diet and smoking is especially important. Smoking is the cause of more than 30 percent of cancer deaths, and diet, too, may be implicated in a great number of cancers. The origins of this group of diseases lie in the interplay between the vulnerability of our genetic material, DNA, and the challenges and stresses that the environment places on the cells in which DNA is housed.
All of that has changed with the discovery of two classes of genes, oncogenes and tumor suppressor genes. The first was discovered through the study of viral cancers in animals, the second through the study of hereditary cancers in humans. The present view of cancer has emerged from a fusion of all three theories. Cancer is a disease of altered genes and altered gene function. These alterations can be inherited or acquired as the result of chemical or physical damage or the effects of viruses.
These new developments in our understanding of cancer are extending to all forms of human cancer. At first, the genetic basis of cancer was observed in certain rare cancers, but now these insights are extending to the most common cancers. Genes whose dysfunction leads to cancer are being rapidly identified. These genes ultimately determine the behavior and the relentless growth of cancer cells. Some of these genes, the oncogenes, can be activated inappropriately, similar to an uncontrolled accelerator of an automobile. Conversely, the tumor suppressor genes, or anti-oncogenes, can lose their function, like defective automobile brakes. Our knowledge about these genes is still incomplete, and many cancer genes remain to be found. Ideas abound on ways to use the new information for cancer prevention, diagnosis, prognosis, detection, and treatment. In short, the whole field of cancer research has been revolutionized and energized by this recent and continuing genetic revolution.
Reducing the burden of cancer can be measured in terms of fewer deaths, fewer new cases, increased length of survival, and increased quality of life of cancer survivors.
For several cancers, decreasing death rates reflect cumulative research successes during the past 25 years, for example, death rates from children's cancers have declined by more than 50 percent. With advances in chemotherapy, hormonal treatments, and in the access to and use of screening mammography, breast cancer mortality has finally begun to decline--down five percent since 1989. Deaths from colon and rectal cancers have dropped steadily, declining 10 percent in the past 25 years, and mortality rates have also decreased for Hodgkin's disease and testicular cancer, both due to dramatic advances in therapy.
After a formidable battle to reduce the prevalence of cigarette smoking, lung cancer rates for men have declined. As smoking rates among women have increased, however, their lung cancer mortality rates have risen alarmingly. For other cancers, including non-
Hodgkin's lymphomas, melanoma, brain, kidney, and prostate cancers, mortality rates have not fallen or are increasing. Particularly disturbing are the higher incidence and mortality rates for many cancers among several ethnic and racial minority populations.
In addition to improvements in mortality rates for many malignancies, we have achieved important improvements in the quality of life for cancer survivors through less disfiguring and less damaging surgical procedures, better pain control, and more effective medication for the side effects of cancer therapy.
Yet, even taking into account these advances, overall cancer incidence continues to increase, emphasizing the formidable task ahead. The goal of a reduced cancer burden can only be achieved by the successful translation of discoveries to the benefit of all people who are at risk for and who have cancer.
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