There are a number of risk factors, most of which cannot be changed. Being a woman is the greatest risk factor - breast cancer affects 1,170 women per million of the population. In comparison, just seven men per million are affected. The risk also increases with age and if family members have suffered breast cancer. Women who start their periods before they are 12 or who go through menopause after they are 50 have a slightly higher risk of breast cancer.
Obesity is a significant risk factor, particularly for men.
The relationship between body fat and cancer is not fully understood, but the extent of the risk is thought to vary depending on when the weight was gained and what sort of fat is consumed. Studies have exposed many other risk factors related to lifestyle, but it is not certain how important these are in determining susceptibility to the disease. Recent American trials suggest the drug Tamoxifen, which is successful in treating breast cancer, may also prevent it. But the trials have proved controversial, with European research showing no evidence to support their findings. The earlier breast cancer is detected, the more chance there is of a full recovery.