As with other cancers, risk is determined by a combination of genetic, environmental, and lifestyle factors. This section looks at these with particular relevance to breast cancer.

Many of these risk factors are outside your control - but it is useful to be aware of them so you can be mindful of whether your particular history may potentially put you at higher risk.  This in turn may motivate you to become more breast-aware and examine yourself regularly.

Age

The single most important risk factor for breast cancer, age, is out of our control.

As we get older, our risk of developing cancer of any type increases and this is particularly seen in the case of breast cancer.  It follows that as our population continues to live longer, the number of women who will inevitably develop the disease will also increase.

A confusing statistic often mentioned is that a womans risk of breast cancer is 1 in 9. This can be misleading, because it refers to the total cumulative risk over an entire lifetime.

Your possibility of developing breast cancer is only 1 in 9 when you are 85.  Half of this chance occurs over 65 and the greatest risk is over 55.  Because older women are at greater risk, preventative measures such as breast screening and education regarding risk are of particular importance to this age group.

Hormonal levels

There are a number of general risk factors associated with breast cancer that are linked to the length of time that female hormones, in particular oestrogen, are manufactured in breast tissue.

What is oestrogen?

Oestrogen is a female sex hormone that is mainly released during the menstrual cycle in pre-menopausal women.  Whilst it serves many important functions in a womans body, ironically it can also be the very thing that some breast cancer cells need to divide and grow and high levels of oestrogen can cause these cells to become cancerous.

How it affects risk

The length of time that you are fertile  in other words, the length of time between your first period and when you enter menopause.  A longer fertile period can increase risk - so, for instance, those who enter menopause at 55 have twice the risk of developing breast cancer than those who enter menopause at 45.  By the same token, the later you started menstruating the better.  An early start to your fertile life ultimately exposes your body to a greater amount of oestrogen over your lifetime.

The age you had your first pregnancy that went to term.  In general, your risk increases if this occurred over the age of 30.  As pregnancy interrupts your menstrual cycles, it follows that it also disrupts oestrogen-level exposure.

The number of pregnancies that you had  fewer than two can also raise the possibility of disease.  In general, increased risk is associated with long periods of uninterrupted menstrual cycles.  This is because in these situations breast tissue is continually exposed to oestrogen.  Clearly, the disruption of oestrogen levels is an important consequence of pregnancy. 

Pregnancy also changes the breast tissue in a way that can prevent breast cells from becoming cancerous.  Therefore, the fewer pregnancies your body experiences, the less beneficial changes occur in your breast tissue.  Breast feeding for at least a year in total also has the effect of changing breast tissue and can be protective.

Family history

Women with a mother and/or a sister with breast cancer have a higher risk of developing the disease - especially if their relations were diagnosed at a young age and developed the condition in both breasts (bilateral breast cancer).

This kind of family history of early onset and bilateral breast cancer suggests the presence of an inherited genetic mutation.  This is uncommon; less than 5% of all breast cancers have a mutation of this kind.

Over the last decade, two genes linked to the inherited disease have been isolated: BRCA 1 and BRCA 2.  Mutations in these genes may also increase the risk of other cancers  for example, mutations in BRCA 2 may confer an increased chance of ovarian cancer.

Both BRCA 1 and BRCA 2 are sizeable genes which produce large proteins likely to have many functions within the cell.  A gene of this size means that there are lots of opportunities for mutations to arise.  Some will occur in incidental areas of the gene and may not have much effect on the resultant protein function.  Others will arise in critical areas, producing a damaged protein unable to perform its normal function within the cell and it is these mutations that researchers are seeking to identify.

It is likely that other genes will also confer an increased risk of breast cancer. Some of these we have identified - such as the p53 gene - but as yet, others remain undiscovered.

Whilst our knowledge is continually expanding there are potentially thousands of mutations yet to be uncovered.  It is worth remembering that current tests are only able to look for those genetic alterations that we already know about.  Although the available testing is effective, it is limited by the current knowledge of genetic alterations related to breast cancer.

Those with an inherited mutation in BRCA 1 or BRCA 2 have a significantly increased risk of breast cancer  but this does not automatically mean that they are guaranteed to develop the disease.  Nevertheless, recent studies have recommended radical surgery for those found to be in this high-risk category.

Benign breast disease

Having a history of benign breast disease does raise your risk of developing breast cancer.  This is because the extra cells present in the breast due to the benign disease may themselves become abnormal.  In practice, this rarely happens, but it is as well to be aware of the possibility if you are prone to benign breast disease.

HRT

HRT refers to Hormone Replacement Therapy  the taking of female hormones to ease symptoms associated with the menopause.  Because breast-tissue exposure to oestrogen can increase the risk of developing cancer, there has been much interest in evaluating hormone replacement after menopause.

Views on the association between HRT and breast cancer are complicated.  In general, use of HRT to alleviate the symptoms of menopause has additional positive and negative implications for overall health.

In other words, the various protective effects for some diseases have to be balanced against the associated heightened risk for other specific conditions when making a decision about taking HRT.

Regarding breast cancer in particular, taking HRT is associated with a small increase in risk which is slightly raised with each year of use.  However, once a woman stops taking HRT her risk reduces again and is back to normal after about 5 years.

Your decision to take or not take HRT is something that will depend on your overall health and the combination of other risk factors relevant to all these diseases that are pertinent to you.  Your GP will be able to advise on what is the most appropriate action for you.

02/06/2009