Although more and more women are surviving, breast cancer is the most common cancer in the UK and it has been on the rise for several years.

In 1999, 42,400 women were diagnosed with the disease. The odds that a woman would develop breast cancer during her lifetime were one in nine.

In 2008, 47,700 women were diagnosed. Taking into account the changing size of the population, this is an increase of around 3.5 per cent in the breast cancer incidence rate. As a result, we’ve now calculated that the lifetime risk of developing the disease is one in eight.

This increase raises the obvious question: why have rates gone up?

Unfortunately there’s no simple answer to this. Breast cancer is a complicated disease with a variety of different causes. Many aspects of our lives swing our risk in one direction or another. Some of these can be controlled, while others are largely out of our hands.

Let’s take a look at some of the possible explanations.

Screening

In recent years, breast cancer rates have risen especially quickly among women aged 65-69. This probably coincides with the inclusion, from 2004, of women in this age group in the national breast screening programme. An increase in the number of women attending screening would be very likely to lead to an increased number of cancers being detected.

In many ways, this is to be expected. Screening programmes are meant to detect cancers at an early stage when they’re too small to cause any symptoms. At this point, they are easier to treat successfully. So you would expect rates to go up when a new group of women is invited for screening.

The screening programme has attracted a lot of recent controversy. Critics say that it picks up a large number of cancers that would never go on to cause a woman any problems. These include a type of cancer called ductal carcinoma in situ (DCIS) – a ‘pre-cancerous’ type of tumour that has not yet started to spread. But our new analysis doesn’t include cases of DCIS, so these non-invasive tumours can’t explain the rising breast cancer rates in women aged 65-69.

Lifestyle

Several aspects of our daily lives can affect the risk of breast cancer. We know that alcohol can cause breast cancer, and even drinking small amounts can increase the risk of this disease. Alcohol boosts levels of oestrogen in the blood, and abnormally high levels of this hormone have been linked to breast cancer.

Large studies have found that drinking an extra unit every day (and remember there are two units in a medium-sized glass of wine) can increase the risk of breast cancer by around 10 per cent. That’s not a big effect, but because the disease is so common, it translates to a surprising number of extra breast cancer cases. For example, the Million Women Study estimated that if everyone drank one extra unit a day, we would see 11 extra breast cancers in every thousand women. The study calculated that 11per cent of breast cancers in the UK are caused by alcohol.

After the menopause, women who are overweight or obese have a higher breast cancer risk than those who have a healthy weight. The Million Women Study also looked at body weight, and calculated that obesity accounts for 7 per cent of the UK’s breast cancer cases. The nation’s expanding waistline could be contributing to the rise in breast cancer rates.

Body fat is surprisingly active, pumping out oestrogen and other hormones that affect how our cells grow and divide. This source of oestrogen becomes increasingly important after the menopause when the ovaries stop producing the hormone.

On the flipside, keeping physically active could reduce the risk of breast cancer by anywhere from 20 to 40 per cent. Researchers are still trying to find out exactly what causes this effect, but again, the evidence points to our hormones.

HRT

We know that hormone replacement therapy can increase the risk of breast cancer although it’s not clear how much this accounts for the recent trends.

The use of HRT rose sharply in the UK between 1992 and 2001. At that point, around a quarter of women aged 45-69 were using HRT. However, the medication’s popularity soon plummeted as it became clear that it was linked to breast cancer.

We know that the longer a woman takes HRT, the higher her risk of breast cancer becomes, and it takes around 5 years for that risk to return back to normal after stopping. So the recent climbing rates could partially reflect the aftermath of prolonged HRT use.

Children

People often forget this when talking about breast cancer, but having children protects against the disease. Women are less likely to develop breast cancer if they have their first child at an earlier age. Their risk also goes down the more children they have and the longer they spend breastfeeding.

These simple associations can explain a lot of the differences in breast cancer rates between developed and developing countries. One study calculated that if women in the Western world had the same number of children as women in the developing world (and breastfed as long), the rates of breast cancer would halve.

Age

People are living longer now than ever before. And one of the risks for most cancers is simply getting older. But it should be noted that the 1 in 8 figure is a lifetime risk – and that during a lifetime, risk changes. For breast cancer, risk increases sharply from around the time of the menopause – see the table below:

Up to and including age Risk (women) 29 1 in 2000 39 1 in 215 49 1 in 50 59 1 in 22 69 1 in 13 Lifetime risk 1 in 8

Other possible explanations

There are many other potential causes of breast cancer – some are myths, others have some truth to them. We’re only going to touch on some of them briefly here, but you can click through for more information.

The Pillprobably hasn’t had a big effect on breast cancer rates. It only slightly increases the risk of breast cancer. Women take it at a young age when their natural risk is low, and that risk disappears quickly when women go off the Pill.

Our dietcan affect our risk of cancer. But despite hundreds of studies and countless books or magazine articles, there’s no clear advice for eating your way to a lower breast cancer risk (other than cutting back on alcohol and keeping a healthy body weight). Studies have looked at everything from fruit and vegetables to dairy products and they have either refuted a link to breast cancer, or found inconsistent results.

Working on night-shifts could affect the risk of breast cancer, according to the International Agency for Research into Cancer. Many scientists are now trying to work out if this is actually true. The problem is that few of the studies to date have accounted for other things that can affect breast cancer risk, like number of children or body weight.

Vitamin Dis a hot topic but despite repeated claims, the evidence linking it to breast cancer is uncertain. Recently, several groups have gathered all the available evidence and when they considered the best studies, they found no link between vitamin D and breast cancer.

Deodorantswere originally linked to breast cancer in an email hoax, and there’s no convincing evidence that they could cause the disease. Nor is there solid evidence for other types of cosmetic products.

Stresscan alter the levels of hormones in the body and affect the immune system. But there’s no consistent evidence that these changes could lead to breast cancer. However, stressful situations can make people take up unhealthy behaviours such as smoking, heavy drinking or overeating that can themselves increase the risk of cancer.

Chemicals in our environment probably don’t play a significant role. There’s been a lot of controversy over the role of man-made chemicals that can mimic oestrogen and, theoretically, cause breast cancer. This is an active area of research and debate, but at the moment there’s not enough evidence from studies in humans to suggest that these chemicals play a significant role in increasing rates of breast cancer.

Large organisations like the World Health Organisation (WHO) and the International Agency for Research into Cancer (IARC) have estimated that pollution and chemicals in our environment only account for about 3 per cent of all cancers. Most of these cases are in people who work in certain industries and are exposed to high levels of chemicals in their jobs.

The good news

While it’s worrying that women are now more likely to develop breast cancer than they were a decade ago, there is good news too.

Survival rates have also shot up. Almost two out of every three women with breast cancer now survive the disease beyond 20 years, compared to less than half in the 1990s.

And more than three-quarters of women diagnosed with breast cancer survive for at least 10 years or more. Research has been at the heart of this progress – and it will continue to play a vital role in beating the disease in the future.

Ed

(Edit, 07/02 – thanks for all the comments and questions, we’ve responded to these here)

Further reading

http://info.cancerresearchuk.org/spotcancerearly/cancersymptomvideos/spotbreastcancerearly/