Health Centres - Breast cancer
What is breast cancer?
The breast is a gland that consists of breast tissue supported by connective tissue (flesh) surrounded by fat.
The easiest way to understand how the inside of the breast is formed is by comparing it to an upturned bush. Its leaves are known as lobules and they produce milk that drains into ducts that are the branches of the breast tree. These in turn drain into 12 or 15 major or large ducts which empty onto the surface of the nipple, just like the branches of a tree drain to the trunk.
Breast cancer develops from the cells that line the breast, lobules and the draining ducts.
Cancer cells that remain confined to the lobule and the ducts are called '
An invasive cancer is one where the cells have moved outside the ducts and lobules into the surrounding breast tissue.
How common is breast cancer?
Breast cancer is the most prevalent cancer among women and affects approximately one million women worldwide.
Breast cancer accounts for 30 per cent of all female cancers in the UK and approximately 1 in 9 women in the UK will get breast cancer sometime during their life.
What are the risk factors leading to the development of breast cancer?
Approximately a quarter of breast cancers affect women under the age of 50, a half occur between the ages of 50 and 69 and the remaining quarter develop in women who are 70 years or older.
Geographical variation
Recent, age-adjusted figures show that the rate of breast cancer per 100,000 women is 24.3 in Japan and 26.5 in China compared to 68.8 in England and Wales and 72.7 in Scotland and 90.7 in North America in white females.
However, studies of women from Japan who emigrate to the US show that their rates of breast cancer rise to become similar to US rates within just one or two generations, indicating that factors relating to everyday activities are more important than inherited factors in breast cancer.
Reproductive factors
Age at first pregnancy
The highest risk group are those who have their first child after the age of 35 and these women have an even higher risk than women who have no children. These observations indicate a 'menstrual cycle effect'. During the monthly cycle a woman's fluctuating hormone levels cause several changes within breast tissue, which are repeated every month.
These changes possibly encourage or amplify abnormalities in the cell repair processes within breast tissue, which can in some cases lead to breast cancer later in life.
Women who have fewer menstrual cycles before their first pregnancy, either through being older when they start menstruating or younger when they first get pregnant, run less chance of such an abnormality occurring.
Inherited risk
It is not yet known how many breast cancer genes there are, but to date, two specific breast cancer genes have been identified (BRCA1 and BRCA2).
There is quite a difference in incidence and death rate of breast cancer between different countries. The biggest difference is between Eastern and Western countries.
Women who start menstruating early in life or who have a late menopause have an increased risk of breast cancer. Women who have natural menopause after the age of 55 are twice as likely to develop breast cancer as women who experience the menopause before the age of 45.
Having no children and being older at the time of the first birth both increase the lifetime incidence of breast cancer. The risk of breast cancer in women who have their first child after the age of 30 is about twice that of women having their first child before the age of 20.
Up to 10 per cent of breast cancer in Western countries is due to an inherited factor. This factor can be passed on from either parent and some family members pass on the abnormal gene without developing cancer themselves.
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