What You Need to Know. What You Can Do.
How have cancer trends changed over the past few years?
On completion of this section, you will be able to
The yearly rate of new cancer cases increased between 1975 and 1992, as the graph below shows. Note some evidence of a decline after 1992 followed by stable rates since 1995. In this graph, scientists use the term incidence to describe the number of persons who develop cancer out of 100,000 persons within a certain period of time.
Increases in incidence rates are sometimes difficult to interpret. An increase in the number of new cases of cancer may result from exposure to a harmful substance in the environment. But increasing incidence may also reflect changes in clinical practice in hospitals or doctors’ offices. These changes result in more cases being found—perhaps even some cases that would never produce symptoms of the disease. Decreases in incidence, on the other hand, are probably due to a decreased exposure to harmful substances or to early detection and removal of precancerous growths.
For cancer deaths, the graph bellow shows that the rates increased steadily from 1975 to 1990, stabilized between 1990 and 1994, then declined on average 1.4 percent per year from 1994 to 1998. Since 1998, the rates again stabilized. In this graph, mortality is the number of cancer deaths that occur out of 100,000 cases within a certain period.
This is very good news: decreases in mortality are the best measure of progress against cancer. Mortality rates would be expected to decrease with a reduction in risk factors (stopping smoking and less exposure to certain pesticides, organic solvents, and asbestos fibers), successful early screening efforts (mammography, Pap test, and fecal occult blood test), or better treatments.
|Changing Rates for Specific Cancers||
In recent decades the incidence and mortality rates for some cancers have been declining. These include testicular, childhood, cervical, stomach, throat, and cancers of the mouth (lip, tongue, gums). For example, in the last 25 years, mortality rates for childhood cancer (ages 1–14) and cervical cancer have nearly halved. Improvements in treatment are thought to account for the reduction in childhood cancer deaths, while increased screening (i.e., Pap smears) accounts for the decrease in cervical cancer rates. The incidence and mortality from stomach and colon cancer and cancers of the mouth and throat have also decreased over this period.
On the other hand, the incidence and mortality rates for certain cancers have not improved. From 1973 to 1999, the incidence rates for cancers of the breast, lung (in females), bladder, prostate, kidney, liver, esophagus, and brain increased, as did non-Hodgkin’s lymphoma and melanomas of the skin. The larger percentage increase in lung cancer incidence rates for women compared with men reflects the fact that women began smoking later in the last century than did men—few women smoked before the 1960s. Over that same 26-year period death rates for melanomas of the skin, non-Hodgkin’s lymphoma, and liver, kidney, lung, and brain cancers also increased.
The more recent trends from 1992–2000 are shown in the graphs below. Today, for women, over half of the new cancer cases and deaths are due to breast, lung, and colon/rectal cancers. For men, more than half of the new cancer cases and deaths are from prostate, lung, and colon/rectal cancers. Scientists are eager to understand these trends as an aid in developing effective cancer-prevention strategies.
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