The biggest risk of all is one we can do nothing about - ageing. Breast cancer is a rare disease in women under 30, but the chances of getting it increase with age.
Our modern life-style also seems to have some connection: environmental campaigners raise questions about the use of chemicals in food production, industrial processes and pharmaceuticals. Whatever the reasons, breast cancer has greatly increased this century and is more a disease of the industrialised countries than of the less developed regions.
Studies of Japanese who migrated to Hawaii show that within one or two generations, their rates of breast cancer rose to the same rates of the host country, America, suggesting that environmental factors far outweigh their genetic counterparts.
Even so, experts suggest that up to ten per cent of breast cancer in Western countries is due to genetic disposition. Two hereditary breast cancer genes have been identified - BRCA1 by the Americans in 1994 and BRCA 2 at Christmas 1995 by an International team led by Cancer Research Campaign-funded scientists. "There are more genes out there waiting to be discovered," says Professor Gordon McVie, the charity's director general.
A woman's risk of breast cancer is doubled if she has a first degree relative (mother, sister or daughter) who developed the disease before the age of 50, and the younger the relative, the greater the risk.
It also seems probable that hormones are involved. Oestrogen appears to play a crucial role, perhaps by increasing cell division in breast tissue, which may set the stage for cancer. Doctors believe that risk rises with certain factors that result in increased oestrogen production or longer than usual exposure to oestrogen.
Women who start menstruating early in life or who have a late menopause have an increased risk of developing breast cancer. So, too, do those who have no children, or who delay childbearing until their thirties. The risk of breast cancer in women who have their first child after the age of 30 is about twice that of women who have their first child before they are 20.
Some preliminary research links an increased risk with short menstrual cycles (less than 26 days), miscarriage, ectopic pregnancy and abortion. Some studies suggest breast-feeding may have a protective effect, although a recent US study found that a history of breast-feeding appeared to reduce risk only until menopause.
Doctors are uncertain about the effects of oral contraceptives and hormone replacement therapy (HRT) because some studies indicate an increased risk while others do not.
Research suggests that there could be a slightly increased risk of breast cancer if HRT is taken long term - for ten years or more. However, this has to be weighed against the other health benefits of HRT.
And at the other end of the female fertility cycle there is some evidence to suggest that young women who take the Pill for four years or more before having a first baby may increase their risk of pre-menopausal breast cancer. On the other hand, the women studied were taking higher-dose oral contraceptives than are in use now. In addition, since the use of oral contraceptives by young women was not common until the 1970s, it is too early to say whether there might be any links between the Pill and developing breast cancer after the menopause.
There is evidence of higher rates of breast cancer among women whose breast tissue was exposed to moderate or high doses of ionising radiation during treatment for other diseases or in the workplace.
Other factors which may possibly increase risk are still under evaluation. These include stress, diet, weight, and high alcohol intake.
Although there is a close correlation between the incidence of breast cancer and a high fat diet in populations, there is still much debate about the the true relation between fat intake and breast cancer. Some studies suggest that a high-fat diet increases risk and that a low-fat, high-fibre diet reduces risk, but other have found no links.
Researchers have found lower rates of breast cancer among eaters of broccoli, cauliflower and cabbage, and vegetables high in vitamins A and C, although there is no proof vitamins A and C supplements provide protection.
Being overweight may be significant, although the evidence is not clear- cut. A higher risk was previously associated with obesity after the age of 50, but the reverse was apparently true for pre-menopausal women. However, US researchers have more recently suggested that gaining just ten pounds in weight after the age of 30 could increase the risk by 23 per cent, while gaining 20 pounds could increase it by 52 per cent.
Some studies have shown a link between alcohol consumption and incidence of breast cancer, but experts add that the relation is inconsistent and the association may be with other dietary factors rather than alcohol.
What can you do to lower the risks?
Reduce your fat intake and increase your consumption of fruit, vegetables and fibre.
Watch your weight and your alcohol intake. Exercise.
Amend your family planning strategy. Breast-feed your children.
If your family history suggests you may be at risk, discuss this with your GP who can refer you for genetic counselling.
Many women who develop breast cancer have no identifiable risk factors. For most of us the best form of defence against the disease is vigilance: be breast aware; take part in the screening programme if you are over 50; see your doctor if you detect any changes in your breast.Reuse content