The Biology of Cancer


Cancer is caused by cells in the body which divide too rapidly by mitosis. A normal cell can turn into a cancer cell if it is exposed to a carcinogen. A carcinogen is a chemical that can cause cancer, by altering the DNA in a cell.

Normal cells have genes called proto-onco genes (literally "before cancer genes") that control cell division. A carcinogen can change these genes into oncogenes that cause cancer. This diagram shows the 3-D structure of the protein produced by an oncogene:

Cells do have natural protection against cancer: genes called tumor-suppressor genes block the cell cycle, and even kill the cell, if the DNA is damaged and the cell starts to divide too rapidly.

In other works the tumor-suppressor genes stop cancer as soon as it starts.

This means that to actually come down with cancer, you typically have to have:

a) a proto-onco gene changed into an oncogene
b) one or more tumor-suppressor genes disabled


The photos below show you the difference between normal cells in the left photo ( in this case in the colon, or large intestine) and cancer cells in the right photo:

Note that cancer cells form a dense mass, or tumor, because they divide so rapidly.





Causes of Cancer

Although cancer is caused by changes in the DNA, typically cancer is more affected by lifestyle ( for example diet and smoking) than by genetics. For example, people who move from one country to another typically pick up the cancer patterns of the new country. Stomach cancer is very common in Japan, but rare in Japanese who move to the US.
Some carcinogens are called "complete carcinogens": they can cause cancer by themselves. Two examples are cigarettes and asbestos, both of which increase the risk of lung cancer.

Asbestos was used in the 1950s and 1960s as insulation in a lot of buildings, including schools. Many states are now removing the asbestos from older buildings, and the workers that do this lovely job have to wear complete protection against the asbestos fibers.

Different types of cancer are caused by different carcinogens. Some types of cancer are relatively mild, and have a high cure rate, for example non-melanoma skin cancer. Very few people die of this type of cancer, so it is not included in most cancer statistics. In contrast, lung cancer has a very low cure rate ( roughly 14%), and is the biggest killer in terms of cancer in the US. (Heart attacks kill more men and women than all types of cancer combined).

Apart from chemical carcinogens, some types of cancer are caused by radiation. Radiation is given off by radiactive materials (eg atom bombs, nuclear power stations, certain natural rocks like granite), but it also includes solar radiaiton from the sun.

Average Daily solar radiation in the United States




Solar radiation does not penetrate far into the body, but exposure to ultra-violet does increase the risk of skin cancer, especially among light-skinned people (this is why Australia has the highest rate of skin cancer in the world).
Other types of radiation include low level ionizing radiation, which is found in building materials, fertilizers and X-rays, for example. Although a lot of people are concerned about pollution by industrial chemicals, this only accounts for about 5% of cancer. A much higher percentage of cancer is caused by diet ( 30% of cancer) and smoking ( 32 % of cancer). To get more information about diet, click here (Centers for Disease Control).