Breast Cancer: Breast Cancer Risk Factors
Breast Cancer Risk Factors

Breast cancers are well known to be affected by the levels of the female hormone, oestrogen which is why a large number of the factors that can affect the development of breast cancer (such as reproductive age, menopause, obesity, alcohol and physical activity) have a direct impact on oestrogen development.

These, however, are not the only factors influencing the risk of developing breast cancer and here I will go through each of the risk elements in turn, taking them in order from the most important to the least important. The statistics presented here represent the developed world (for the most part Europe and North America), however, I do try and point out, where relevant, where lifestyle, dietary or behavioural differences elsewhere in the world make an impact on their survival rates.


Acne Pimples
The image above shows an example of a lump in a female breast (the lump is circled). The image itself is of a mammogram that has been digitally enhanced and withiout this enhancement the lump would not have been seen or detected.

Breast Cancer and Gender

Obviously gender is the most important factor, and though men can develop breast cancer only a very small percentage do and they tend to be carrier of one of the breast cancer genes.


Breast Cancer and Age

By far the strongest risk factor for the development of breast cancer is age. The table below shows the overall lifetime risk of developing breast cancer at various ages:

AgeLifetime Risk
Up to 251 in 15 000
Up to 301 in 2 000
Up to 401 in 200
Up to 451 in 50
Up to 501 in 15 000
Up to 601 in 23
Up to 701 in 15
Up to 801 in 11
Up to 851 in 10

Throughout a woman's lifetime, the overall risk of developing breast cancer is 1 in 9 (assuming she reaches her 90s). However, the actual risk for any given woman is 7 per 100 (ie 7%).


Reproductive History

Overall, women in developing countries are at significantly lower risk of developing breast cancer than women in developed countries. Part of this is due to higher mortality, so women do not reach advanced ages in developing countries. However, another major difference is due to different reproductive histories. Indeed, it's estimated that if Western women had the same reproductive histories as women in developing countries the overall incidence of breast cancer in the developed countries would fall from 7 per 100 to 3 per 100.

The effects are cumulative throughout a woman's life and follow her entire reproductive history.


Age at Menarch

This is the age at which a woman begins menstruating and is first sexually receptive. Better nutrition in developed conutries has lead to the age of menache falling from around 16–17, as it was in the 19th century to 12—13 today. This is why China, with a later average menache of 16–17 years has a much lower risk of breast cancer. Indeed, it's been estimated that breast cancer risk is lowered by 7% for each year that menache is delayed after age 12.

Age at First Birth

The younger a woman is when she first gives birth, the lower the risk of breast cancer in later life. The risk of developing breast cancer has been estimated as increasing by 3% for each year that the first baby is delayed. For example, a woman who has her first child at age 25 would have a 9% lower risk than a woman who has her first child at age 28.

Parturition

The act of giving birth itself quite dramatically reduces the risk of breast cancer. Indeed, it's been estimated that a woman who has never given birth has a 30% greater risk that a woman who has given birth to a child.

Beyond this, the number of live births also has an influence and it's been estimated that each child after the first reduces a woman's risk of breast cancer by 7% (in the absence of breast feeding [see below])

Breast Feeding

The act of breastfeeding itself also confers a protection against breast cancer. Not only is it good for the child, it's good for the mother as well. What's less well known is that the duration of breast feeding has an impact.

This also explains one of the factors affecting the difference between developed and developing countries in terms of breast cancer prevalence. In developed countries women typically breast feed for 9 months, but in developing countries it tends to be more like 24 months and analyses indicate that the incidence of breast cancer falls by 4.3% for every year that a woman breast feeds.

Age at Menopause

Again, better nutrition in developed countries has meant that women typically undergo menopause later. Late menopause is a known risk factor for breast cancer. Indeed, for every year that menopause is delayed there is a 3% increase in the risk of developing breast cancer.


Hormones and Breast Cancer

As breast cancer risks are known to change with the levels of oestrogen in a woman's body a number of studies have examined the influence of hormones from outside the body on the incidence of breast cancer. Typically these comes from use of contraceptive pills and the use of hormone replacement therapy (HRT) post menopause.

The Contraceptive Pill

Large-scale trials on women taking the contraceptive pill indicate that the risk of developing breast cancer is 23% greater in a woman actively taking the pill. Up to 4 years after stopping taking the pill the risk is 15% greater. Up to 9 years after taking the pill the risk is 6% greater and 10 years after taking the pill there is no difference.

As a result it can take up to ten years for the effect of the pill to disappear from a woman's reproductive history.

Hormone Replacement Therapy (HRT)

HRT has two effects. It increases the risk of breast cancer and it also makes breast tissue more dense which makes mammography more difficult and thus makes the diagnosis of breast cancer more problematic.

In current users of HRT the risk increase depends on the type of drugs used. If a woman is taking only oestrogen then her risk is 30% increased compared to a woman not taking hormone therapy. But if a woman is taking a combination of oestrogen and progesterone her risk is 100% increased (doubled) as compared to a woman not taking the therapy.

Five years after stopping therapy the risk is about 8% increased and at 10 years after therapy there is no increased risk.

There is now debate about the benefits of HRT. Indeed, with almost 20 million women now taking some form of HRT the increased incidence of breast cancer is beginning to out-weigh the benefits from reduced incidence of colorectal cancer and hip fracture.


Natural Hormones

In some women, post menopause, their levels of the sex hormone, oestradiol increases and studies (though still quite preliminary) indicate that those women with the highest level of this hormone had an almost doubled risk of developing breast cancer.


Obesity and Breast Cancer

Recent studies have shown that post menopause, significantly overweight women have up to a two-fold increase in the risk of breast cancer compared to woman of normal weight.

This is probably due to a consequence of the menopause itself. At the menopause the ovaries stop producing oestrogen. As a result, adipose (fat) tissue is the main source of oestrogen in post-menopausal women. The more fatty tissue that a woman has, the more oestrogen she produces. Conversely, obesity is also linked with lower levels of sex hormone binding globulin, whose job is to clear excess oestradiol from the body. As a result the levels of oestradiol increases and this, in turn, leads to greater risk of breast cancer.


Breast Cancer and Exercise

Recent studies have focussed on the importance of exercise in determining breast cancer risks. These studies strongly indicate that physical activity can have a preventative effect of between 30 and 40% in terms of lowering the risk of breast cancer (and this with just a few hours' vigourous activity each week).

The reason for this effect is unclear, though it may be that exercise reduces the risk of obesity and it's this that produces the beneficial effect (see above).


Alcohol and Breast Cancer

Studies have quite consistency shown a clear link between alcohol intake and the risk of breast cancer. The effect seems to be a 7% increase in risk for every unit of alcohol drunk on a daily basis. For comparison, a bottle of wine drunk every day would give you about a 70% increase.


Diet and Breast Cancer

It was once thought that a diet high in fat, particularly saturated animal fats, played a significant role in breast cancer and was a major risk factor. However, comparisons with other cultures and new studies strongly suggest that though high fat intake does play a role in increasing the risk of breast cancer the actual effect is nowhere near as great as it was once thought to be.


Height and Breast Cancer

This is an unusual one... There is a strong correlation between height and breast cancer. Taller women have in increased risk of breast cancer. Over 1.6m there seems to be an increased risk of approximately 7% for each additional 5cm in height.

Most scientists have been puzzled by this finding with genetic and environmental factors being posited as a risk factor. However, increased height in the human population as a whole has to do with increased nutrition and, as already explained above, improved nutrition is linked to earlier menache and later menopause, both significant risk factors for breast cancer.

Though it's not fashionable to say so, taller women also tend to marry later and bear children later. As a result they also tend to fall foul of these breast cancer risk factors.

Given these explanations it's probably not that surprising that breast cancer risk is correlated with being tall.


Socio-economic Status and Breast Cancer

Breast cancer risk is linked to social class, but unlike most other diseases the link is an inverse one. The more affluent you are, the greater your risk of breast cancer is. Of course, the reasons behind this probably lie with reproductive history and early nutrition.


Breast Density and Breast Cancer Risk

The density of the breast is determined by the precise mix of tissues that go into its formation: fat, connective tissue and epithelial tissue. Breasts with a higher proportion of fatty tissue are much less dense, for example.

Increased breast density seems to result in a 2–6-fold increased risk of breast cancer as compared with women who have less dense breasts. It's also true that it's more difficult to detect the early stages of cancer in women with denser breasts.


Breast Disease and Breast Cancer

Throughout her life a woman may be prone to several different kinds of breast disease. Some of these have no influence on the development of breast cancer whereas others are associated with an increased risk. These diseases are listed below:

Younger women may develop breast lumps. However, by and large, these tend to be caused by fibroadenomas and are not associated with any increased risk of later developing breast cancer.

In their 30s and 40s women may develop breast cysts. Those individuals who tend to develop multiple cysts seem to be at a slightly increased risk as compared to those who do not develop cysts, but the difference is small.

Women who have developed breast lumps and where biopsies have shown these to be due to proliferative breast disease (but without atypia) have a 2-fold increased risk of developing breast cancer. However, women where biopsies have revealed atypical hyperplasia have around a 4-fold increased risk.


Family History of Breast Cancer

Much has been published in the press and on-line about the so-called breast cancer genes, BRACA1 and BRACA2 as a result many women are unnecessarily concerned that a family history of breast cancer necessarily means that they may be carrying one of these genes. Here, then, are the real facts:

In purely statistical terms, having a first-degree relative (that is a mother or sister) with breast cancer doubles your risk of developing breast cancer. However, it should be pointed out here that over 85% of women who have a close relative with breast cancer never develop the disease. Conversely, over 85% of women who develop breast cancer have no family history of the disease.

Indeed, recent studies indicate that heredity only accounts for 25% of the risk factors for the development of the disease 75% of all risk factors are associated with lifestyle (such as the risk factors already described above).

Only a very small minority of women have a very strong family history of breast cancer and, as a result, are at a very high risk of developing the disease themselves. In the vast majority of cases those at the highest risk tend to have mutations in one or other of the breast cancer susceptibility genes: BRCA1 or BRCA2 (mutations in these genes account for about 4% of all breast cancers). However women with a mutation in one of these genes have between a 50% and an 80% chance of developing the disease.

Indeed, only if you have several relatives with early onset of breast cancer is there a significant inherited predisposition towards the disease. For the vast majority of women family history is not an important factor.


Re-ocurrence of Breast Cancer

A woman who has already had breast cancer is about 4 times more at risk of developing a second primary cancer compared with a woman who has not had breast cancer.