Does Tamoxifen help prevent breast cancer?
Breast cancer is the uncontrolled growth of cells in the breast. It occurs as a result of mutations in the genes responsible for the growth of cells. The genes are located in the cells' nuclei, and are the instructions for the whole cell. Normally, cells in the body divide by mitosis and the new cells take over as old ones die out. However, when mutations occur they can activate or deactivate certain genes, changing the cell's ability to control its growth. The cells now divide uncontrollably, producing more mutated cells and forming a tumour.
(Figure 1 shows cancerous cells dividing and a tumour forming) 
Tumours are either benign or malignant. Benign tumours are not usually dangerous to health, and are not considered to be cancerous as they don't spread to other parts of the body, and don't invade other tissues. They can often be removed and in most cases don't return. Malignant tumours are cancerous, and invade and damage other tissues. They metastasize, which means that the cancerous cells break away from the tumour and enter the bloodstream or lymphatic system, forming secondary tumours in different parts of the body. 
Gender Women are at a much higher risk of breast cancer, as their breast cells are constantly changing and growing. This is due to the activity of the female hormones estrogen and progesterone. However, men also get breast cancer, about 370 in the UK each year, compared with 48,400 cases of women
Age The risk of contracting breast cancer increases with age. From age 30 to 39, the risk is 1 in 227, or .44%. That jumps to 1 in 28, or just under 4%, by the time a woman reaches her 60s. (Figure 2 shows the risk of having breast cancer increasing with age) 
Weight After the menopause, fat tissue is the body's main source of estrogen, as the ovaries stop producing it. Overweight people have more fat tissue, and therefore higher estrogen levels, which can...