1.6 - C - Tumours
Tumors are masses of tissue that result from abnormal cell growth. They can develop at any stage of life and result from errors in regulating the cell cycle. Malignant tumors are able to spread through the body (metastasize) and form secondary tumors, which results in cancer.
There are diverse causes. Mutagens are chemical and physical agents can cause gene mutations. If mutations occur in genes responsible for cell cycle regulation, then uncontrolled cell growth can occur. Genes that can become cancer-causing after mutating are known as oncogenes.
Typically, several mutations must occur in a cell in order for it to become a tumor, so the chance of this happening is small. However, there are vast numbers of cells in the body, so the total chance of a tumor forming during a lifetime increases over time.
Each type of cancer that can occur can result from many gene mutations. This vast number of possible oncogenes has made it difficult for scientists to research and develop treatments. However, evolving genetics techniques promises to address this.
Smoking & Cancer
A correlation in science is a relationship between two factors. There is a positive correlation between cigarette smoking and the death rate due to cancer. This has been shown repeatedly in surveys, which indicate that the more cigarettes smoked per day, the higher the cancer death rate. There is even a higher death rate among those who smoked at one time but had stopped.
It is important in science to distinguish between a correlation and a cause. Finding that there is a positive correlation between smoking and cancer does not prove that smoking causes cancer. However, in this case the causal links are well established.
Cigarette smoke contains many different chemical substances, twenty of which have been experimentally shown to cause tumours in the lungs of lab animals and humans. There is evidence that at least forty other chemicals in cigarette smoke are carcinogenic. This leaves little doubt that smoking is a cause of cancer