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What You Need to Know. What You Can Do.
How have cancer trends changed over the past few years?

Learning Objective

On completion of this section, you will be able to

  • Describe changes in trends of cancer incidence and mortality during the past few years.

Introduction

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.



Figure 5. Rates of New Cancers: Annual Percent Change.

U.S. Trends in Rates of New Cancers and Cancer Deaths: 1992-2000

How to read these charts: The charts show the percentage changes in cancer rates for several cancers from 1992–2000. The chart on the left shows the percentage changes in the rates of new cancer cases; the one on the right shows the changes in the rates of cancer deaths. Cancer rates in blue have decreased over this time, while those in red have increased. For example, the incidence rates of liver, thyroid, and melanoma cancers had the greatest percentage increase; the death rates for liver cancer, lung cancer in women, and esophageal cancers showed the largest net increase. Note, however, that both the incidence and mortality rates for prostate and lung cancers (males) have decreased.

Source: SEER (seer.cancer.gov) and NCHS (www.cdc.gov/nchs).



Figure 6. Rates of cancer deaths: Annual percent change.

Key Points

  • The yearly rate of new cancer cases increased between 1975 and 1992. Some evidence shows a decline after 1992 followed by stable rates since 1995.
  • For cancer deaths, the rates increased steadily from 1975 to 1990, stabilized between 1990 and 1994, then declined from 1994 to 1998. Since 1998, the rates again stabilized.
  • The incidence and mortality rates for some cancers have been declining.
  • The incidence and mortality rates for certain other cancers are not improving.
  • 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.
Progress Check

Choose the best answer.

1. Which of the following statements concerning interpreting incidence rates of cancer is INCORRECT?

A. An increase in new cancer cases may result from exposure to a harmful substance in the environment.
B. An increase in new cancer cases may reflect certain changes in clinical practice in hospitals or doctors' offices resulting in detection of more cases.
C. A decrease in cancer incidence may be due to a decreased exposure to harmful substances.
D. A decrease in cancer incidence may be due to late detection and nonremoval of precancerous growths.

Answer:

To review relevant content, see Introduction in this section.

2. Which of the following statements concerning changing rates for specific cancers is INCORRECT?

A. The incidence and mortality rates have been declining for testicular, childhood, cervical, stomach, throat and cancers, and cancers of the mouth (lip, tongue, gums).
B. The incidence and mortality rates are not improving for breast, lung (in females), bladder, prostate, kidney, liver, esophagus, and brain, non-Hodgkin's lymphoma and melanomas of the skin.
C. The larger percentage increase in lung cancer incidence for women compared with men reflects the fact that women smoke more than do men.
D. 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.

Answer:

To review relevant content, see Changing Rates for Specific Cancers in this section.

3. Which of the following statements concerning changing rates for specific cancers is INCORRECT?

A. The incidence rates of liver, thyroid, and melanoma cancers had the greatest percentage decrease between the years 1992 and 2000.
B. The death rates for liver cancer, lung cancer in women, and esophageal cancers showed the largest increase between the years 1992 and 2000.
C. The yearly rate of new cancer cases increased between 1975 and 1992. Some evidence shows a decline after 1992 followed by stable rates since 1995.
D. For cancer deaths, the rates increased steadily from 1975 to 1990, stabilized between 1990 and 1994, then declined from 1994 to 1998. Since 1998, the rates again stabilized.

Answer:

To review relevant content, see Introduction and Changing Rates for Specific Cancers in this section.


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