12.8: Summary

Lung cancer is the leading cause of death from cancer in the U.S., and is mainly due to smoking. There’s a falling trend in cancer death rates when lung cancer is excluded.

Trends in the occurrence of cancer are much harder to assess than trends in cancer deaths. The reasons are many, but a prominent one is that occurrence rates are based on the recorded rates of diagnosis in only certain segments of the population (deaths and causes of death are recorded for the entire population). Trends in cancer rates can be misleading, e.g., cancer rates go up when progress is made against other causes of death such as heart disease, and when more cancer is detected by earlier, more widespread, and/or more sensitive testing.

Cancer is an uncontrolled growth of cells that can have fatal consequences. It’s typically caused by inherited or acquired mutations in genes that control cell growth. Substances that cause such mutations are called carcinogens.

Efforts to determine which substances are carcinogens begin with screening tests such as the Ames test (that uses special bacteria to see if the test substance can cause mutations). This is followed by animal testing. Animal test data are often challenged as to the degree to which they can be extended to humans. We depend on animal studies together with population studies to evaluate human cancer risk.

Because of the complex biology of cancer and the complexity of our heredity and environment, it’s hard to isolate contributing factors and determine the degree to which each plays a role in cancer. In most cases, the best we can do is determine what environmental factors are linked with cancer, and do what we can to lower the risk.

The natural world surrounds us with cancer- causing agents, including ultraviolet light, radio active materials found naturally in soil, and substances found naturally in food. But we aren’t defenseless. As examples, we have melanin in our skin, DNA repair mechanisms, and a very sophisticated immune system.

We can choose to avoid major risk factors such as smoking. Smoking is the cause of most lung cancers and some other cancers.

Alcohol is also a risk factor for various cancers, so avoiding or drinking less alcohol is a way to lower the risk of cancer. Alcohol intake is estimated to be the cause of 15% of breast cancer deaths in the U.S. The link between alcohol intake and breast cancer isn’t widely known among young women. More people are aware that alcohol can damage the liver and increase the risk of liver cancer.

We can follow the dietary recommendations in Chapter 4. Vegetables and fruit seem to be particularly protective against cancer. They are typically high in fiber and low in fat and calories, factors linked to lower cancer risk. Also, vegetables and fruit contain a variety of substances that may protect against cancer.