Family doctor

Do you have a family history of breast cancer?

All patients with a breast health problem are asked about their family history of breast cancer. But what does this mean? What are the family history features that really affect our chances of developing breast cancer?

A family history of breast cancer means having a relative who has had this disease. The importance varies according to the number of affected relatives, their age when they were diagnosed, and how closely related they are to us. As breast cancer is a common disease (affecting over 1600 new women in New Zealand each year), most of us have a relative who has been affected. If this relative was an older or distant aunt, this in fact does not increase our personal risk significantly. If however, a detailed family tree reveals a pattern of breast, ovarian and other cancers, this may have a significant effect on our breast cancer risk.

Over our lifetime, we in New Zealand have approximately a 1 in 10 chance of developing breast cancer. This is similar in Australia, but lower than in the USA.

Who is a close relative?

A close relative is a first or second degree relative on our father or mother's side of the family.

First degree relatives are parents, siblings and children.

Second degree relatives are aunts, uncles, nieces, nephews, and grandparents.

It is estimated that only 5 to 15% of breast cancers occur in families where an inherited genetic mutation is responsible for an increase in susceptibility to breast cancer.

An important fact to remember is that most cases of breast cancer strike out of the blue - affecting otherwise healthy women, who have no known risk factors, not even a strong family history, which may have alerted them to the possibility.

The family history alone can be used to identify three categories of women at differing risks for breast cancer. This information is usually taken into account together with the other known risk factors when assessing a woman's overall risk.

1. The very high risk group

Very high risk women may have inherited a gene from either their mother or their father which makes them more likely to develop breast cancer than other women. In very high risk families the pattern of affected relatives is dramatic. Typically, a sister and/or mother, an aunt (or two), a grandmother and possibly other relatives on the same side of the family have had breast cancer - often at a young age (under 50 years); often both breasts have been involved. Evidence of other cancers such as ovarian, bowel and prostate cancer, and breast cancer in male relatives is seen. This situation affects less than 1% of the population. The lifetime risk of developing breast cancer is over 25%, and up to 85% in a woman known to have the gene mutation. The mutation is passed on to approximately 50% of their children.

After years of careful study the first of a number of specific gene abnormalities was discovered in 1994. Some of these mutations (BRCA1, BRCA2) can now be tested for, once a thorough family history has been compiled, and the appropriate counselling has been completed. Gene testing may provide information that is a helpful guide to future management decisions.

If you are concerned that your family fits the above description, ask your Family Doctor to refer you to a local specialist genetics service for further evaluation.

2. The moderately increased risk group

Four percent of the female population is at moderately increased risk of breast cancer due to family history. Here a family tree may reveal breast cancer in one or two first degree relatives (mother, sister, daughter) before the age of 50. Or there may be two close relatives on the same side of the family with breast or ovarian cancer. Several genes are associated with this risk category, but research is still under way and testing is not readily available. The lifetime risk is 15% to 25%. While women in this situation may find this very worrying, 75-90% of women in this group will not get breast cancer.

3. The average or slightly above average risk group

Having a close relative who was diagnosed with breast cancer over the age of 50 years, does increase our risk, but only to a very small extent (1.5 times normal). This equates with a lifetime risk between 10 and 15%. More than 90% of women in this group will not get breast cancer.

It is important to consider that, while most women with breast cancer have no particular risk factors, simply being female and advancing in age confers a risk that we all carry. Much research is underway to determine what causes breast cancer, and to identify women who are at risk higher than the general population. This holds great promise for the future, but for now we rely on awareness and early detection to ensure effective treatment and improved survival from this disease.

Early detection

Early detection relies on all women being well informed about breast cancer, promptly reporting any breast changes, attending for yearly breast examinations from age 35, and having yearly mammograms from age 40 years. Women at increased risk are advised to discuss additional surveillance strategies such as breast ultrasound, more frequent examinations, and gene testing with a breast specialist.