WHAT IS CANCER?
Cancer is the second leading cause of death, after heart disease. In the United States, cancer is responsible for almost one in four deaths, claiming nearly 1600 lives every day. Evidence indicates that most cancers in the United States could be prevented by simple changes in lifestyle. Tobacco use is responsible for about 30% of all cancer deaths (Figure 12.1). Diet and exercise, including their relationship with obesity, account for another 30% of cancer deaths.
Cancer is the abnormal, uncontrolled multiplication of cells, which can ultimately cause death if left untreated.
Most cancers take the form of tumors, although not all tumors are cancerous. A tumor (or neoplasm) is a mass of tissue that serves no physiological purpose. It can be benign, like a wart, or malignant, like most lung cancers.
Benign (noncancerous) tumors are made up of cells similar to the surrounding normal cells and are enclosed in a membrane that prevents them from penetrating neighboring tissues. They are dangerous only if their physical presence interferes with body functions.
The term malignant tumor is synonymous with cancer. A malignant tumor can invade surrounding structures, including blood vessels, the lymphatic system, and nerves. It can also spread to distant sites via the blood and lymphatic circulation, producing invasive tumors in almost any part of the body. A few cancers, like leukemia (cancer of the blood) do not produce a mass but still have the fundamental property of rapid, uncontrolled cell proliferation.
Every case of cancer begins as a change in a cell that allows it to grow and divide when it should not. A malignant cell divides into new cells without regard for normal control mechanisms and gradually produces a mass of abnormal cells, or a tumor. It takes about a billion cells to make a mass the size of a pea, so a single tumor cell must go through many divisions, often taking years, before the tumor grows to a noticeable size. Eventually, a tumor produces a sign or symptom that is detected. In an accessible location (such as a testicle), a tumor may be felt as a lump. In less accessible locations (such as the lungs), a tumor may be noticed only after considerable growth has taken place and may then be detected only by an indirect symptom, such as a persistent cough or unexplained bleeding or pain.
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Answers (Test Your Knowledge)
1. All three. These and many other fruits and vegetables are rich in phytochemicals, naturally occurring substances that may have anti-cancer effects.
2. True. Although rare, testicular cancer is the most common cancer in men between ages 15 and 35. Regular self-exams may aid in its detection.
3. True. The primary cause of cervical cancer is infection with the human papillomavirus (HPV), a sexually transmitted pathogen. The use of condoms helps prevent HPV infection.
Metastasis, the spread of cancer cells, occurs because cancer cells do not stick to each other as strongly as normal cells do and therefore may not remain at the site of the primary tumor, the cancer’s original location. They break away and can pass through the lining of lymph or blood vessels to invade nearby tissue. They can also drift to distant parts of the body and multiply, establishing new colonies of cancer cells.
This traveling and seeding process is called metastasizing, and the new tumors are secondary tumors, or metastases.
The ability of cancer cells to metastasize makes early cancer detection critical. To control the cancer, every cancerous cell must be removed. Once cancer cells enter either the lymphatic system or the bloodstream, it is extremely difficult to stop their spread to other organs.