Cancer may affect people at all ages, even fetuses, but the risk for most varieties increases with age.[1] Cancer causes about 13% of all deaths.[2] According to the American Cancer Society, 7.6 million people died from cancer in the world during 2007.[3] Cancers can affect all animals.
Nearly all cancers are caused by abnormalities in the genetic material of the transformed cells. These abnormalities may be due to the effects of carcinogens, such as tobacco smoke, radiation, chemicals, or infectious agents. Other cancer-promoting genetic abnormalities may be randomly acquired through errors in DNA replication, or are inherited, and thus present in all cells from birth. The heritability of cancers are usually affected by complex interactions between carcinogens and the host's genome. New aspects of the genetics of cancer pathogenesis, such as DNA methylation, and microRNAs are increasingly recognized as important.
Genetic abnormalities found in cancer typically affect two general classes of genes. Cancer-promoting oncogenes are typically activated in cancer cells, giving those cells new properties, such as hyperactive growth and division, protection against programmed cell death, loss of respect for normal tissue boundaries, and the ability to become established in diverse tissue environments. Tumor suppressor genes are then inactivated in cancer cells, resulting in the loss of normal functions in those cells, such as accurate DNA replication, control over the cell cycle, orientation and adhesion within tissues, and interaction with protective cells of the immune system.
Diagnosis usually requires the histologic examination of a tissue biopsy specimen by a pathologist, although the initial indication of malignancy can be symptoms or radiographic imaging abnormalities. Most cancers can be treated and some cured, depending on the specific type, location, and stage. Once diagnosed, cancer is usually treated with a combination of surgery, chemotherapy and radiotherapy. As research develops, treatments are becoming more specific for different varieties of cancer. There has been significant progress in the development of targeted therapy drugs that act specifically on detectable molecular abnormalities in certain tumors, and which minimize damage to normal cells. The prognosis of cancer patients is most influenced by the type of cancer, as well as the stage, or extent of the disease. In addition, histologic grading and the presence of specific molecular markers can also be useful in establishing prognosis, as well as in determining individual treatments.
Preventing Cancer
Recently, cancer researchers and physicians have devoted time and attention to the preventive aspects of fighting cancer. Early anticancer efforts were directed at treating the disease, but increasingly research has shown that individuals can take steps to prevent cancer. In 1964, the Surgeon General told the country that if we stopped smoking we could greatly reduce our chances of contracting lung cancer. Over the past several decades we have begun to hear other similar messages.
We know that the behavior of the cells in our bodies may be affected by any or all of the following:
- Dietary factors
- Tobacco use
- Environmental agents
- Heredity
While there are no absolute guarantees when it comes to preventing cancer, we know—or have good reason to believe—that lifestyle changes can protect you from cancer. These changes include:
- Stoping smoking and avoiding "second-hand" smoke.
- Eating less fat.
- Eating more fiber.
- Eating more fruits and vegetables.
- Limiting alcohol consumption.
- Wearing sunscreen.
- Exercising.
In this section of the module we will look at four "risk factors" for cancer: heredity, nutrition, smoking, and exposure to the sun. Use the menu below to begin your tour through the world of cancer prevention.
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