What is Cancer?

What is cancer? Are we making any progress on understanding how cancer occurs? A Lakelands Resident

When President Richard Nixon declared war on cancer in 1971, most scientists believed that human cancers were caused by radiation, viruses and chemicals. Our view as to the underlying cause of cancer has changed considerably over the past 27 years. We now understand that while cancer is always genetic in causation, its development is a multistep and interactive process. Changes leading to the malignant state occur within our genes, but only rarely (~10% of cases) is cancer a hereditary condition. More often environmental exposures (smoking, radiation, chemicals) contribute to the accumulation of mutations within our genetic material and most directly influence the onset, variability and progression of the cancer.

The term cancer is used to refer to any number of diseases caused by the abnormal growth of cells in the body. The name given to a particular cancer stems from the tissue or body cells in which it originated, for example a hepatocellular carcinoma is called a liver cancer. Tumors and cancerous masses can grow and develop malignancy from a single abnormal cell in any tissue of your body.

Normally our cells reproduce and divide in an orderly fashion through the cell cycle. This enables our bodies to grow, and to repair worn out or damaged tissue. Regulation of cell growth is accomplished by a very intricate array of chemicals (growth factors, receptors, signaling proteins) each produced by individual genes. Together, there are probably more than 100 different proteins, and therefore genes, involved in cell cycle regulation. Each cell is directed to grow and divide, or to stop growing and differentiate, based on these protein messages in the surrounding environment.

Cancer is a direct consequence of the loss of this cell cycle control. A cancer cell may emerge from within any given population of body cells through the accumulation of mutations in these regulatory genes. These mutations can be caused by radiation or known carcinogens. Gene mutations also can occur spontaneously or be inherited.

Most of the genetic events that lead to cancer occur over the lifetime of an individual. The key initial event or 'hit' usually involves damage to a regulatory gene in one individual cell. This cell begins to divide more quickly and without restraint. The descendants of this cell become further transformed and lose there ability to correct errors. Additional 'hits' in other genes result. In all more than 6-8 different regulatory genes must be 'knocked out' before these improperly formed and dividing cells become cancerous masses known as a tumor.

The stepwise progression of cancer, due to the accumulation of mutations in our genes, has been the most significant contribution to the understanding of the cancer disease process. Although much work remains to be done, this knowledge provides the hope that in our lifetime the war against cancer will be won. Please look for our October column when we will discuss colon cancer in more detail.