Human cells contain a number of gene loci which appear to have as their main function the control of cell differentiation and division. As normal cells divide the ends of the chromosomes are gradually removed so that after a set number of divisions the telomeres as they are called are completely removed. Once this happens no further cell division can occur. The gene loci controlling cell development act in response to the environment in which they find themselves within the body. One group of genes act as main switches to turn off certain other genes in the system, this allows differentiation to occur as the organism develops and maintains the integrity of the tissue once adulthood is reached. When necessary, another group of genes activate the gene system responsible for DNA replication and cell division. If the tissue is not the cells forming the seminiferous tubules in the testes another gene set for removal of telomeres is active so that during cell division the telomeres will be gradually be removed from the chromosomes. This system is fine until a mutation occurs within it. If the genes controlling differentiation (specialisation) are not activated then the tissue will not develop the proper characteristics allowing it to relate to the surrounding tissue and will be generalised. If the genes which switch off cell division are mutated then the cell will rapidly divide without the ability to stop. If the telomere reduction system fails then the cell becomes immortal and will grow in number with no possibility of control. A cancer cell is undifferentiated and immortal with the capability to grow continuously so that it disrupts the surrounding organ structure and finally may cause death. If the cancer is malignant it has the ability to invade surrounding tissue and may release cells into the tissue fluids in which they travel to other parts of the body giving rise to secondary tumours. A tumour is the name for any mass of abnormal cells in an organ. Not all tumours are cancerous and not all are malignant. A wart is a tumour caused by a which contains a gene which deactivates the cell division control system of our cells. A series of mutations must occur in a cell to convert it into a malignant cancer cell and therefore it is understandable that the probability of the incidence of cancer increases with the age of the individual. Certain environmental factors can increase the rate of gene mutation and are therefore likely to increase cancer incidence. Smoking, exposure to dioxin, benzene, many other organic materials, ionising radiation, ultra-violet light and microwaves to name but a few. The infection of cells by certain viruses can cause the formation of oncogenes within the system. Oncogenes are alleles which alter the cells division control mechanisms. Some retroviruses reverse transcribe their DNA into our DNA at sites which result in alteration of the gene code into an oncogene and consequently this causes alteration of the cells division mechanisms.

Protection against cancer involves:

Avoidance of known carcinogens;

Early detection through screening programmes;

Surgical removal of the cancer;

Radiation therapy or chemotherapy depending upon the position and type of cancer.

Cervical cancer: Smear test of the cells of the cervix are taken and examined microscopically to detect cells which have an abnormal structure. A computer recognition system is now undergoing testing to improve recognition rates. The patients being screened are informed of their result after some weeks. If abnormal cells are discovered the cervix is examined with an endoscope and if the affected area is lasered away.

Breast cancer: Occurs in both males and females, although more commonly in the latter. Mammography is the screening technique used. The breasts are squeezed between two plates and x-rays are passed through the flattened breasts. This gives a much more easily recognised image of any abnormal tissue present. Any tumours or cysts will be surgically removed and if found to be malignant the lymph gland up into the armpits may also be taken out. Following this chemotherapy is used to restrict the possibility of secondary tumours developing.

Colon cancer: This cancer is often discovered too late, however a new test has been developed which involves taking a faecal smear sample on a specially formulated toilet paper. This is then sent off to the laboratory and biochemically tested for the presence of blood cells which are found at even the earliest stages of tumour formation. If these are detected then endoscopy is used to view the tumours and these will be surgically removed. Generally at the moment by the time this cancer is discovered it has already spread to other parts of the body. This is the case with many deep body cancers.

Lung Cancer: develops from several causes and has a number of distinct types. Small cell cancer is the most malignant form. Detection is by chest x-rays although this tends not to find the cancer until it is well developed. Endoscopy is also used in cases where symptoms suggest the possibility of lung cancer. Surgical removal of lung tissue and then chemotherapy is necessary.

Melanoma: This skin cancer is extremely malignant and will spread rapidly through the body causing massive damage. It must be surgically removed as soon as possible. It is caused by exposure to ultra-violet light and typically appears as a mole on the skin. The outline is irregular and the cancer induces growth of blood vessels into the area so that growth is particularly fast.