Researchers: Up to a third of breast cancers could be avoided with lifestyle changes

BARCELONA, Spain -- Up to a third of breast cancer cases in Western countries could be avoided if women ate less and exercised more, researchers at a conference said recently, renewing a sensitive debate about how lifestyle factors affect the disease.

Better treatments, early diagnosis and mammogram screenings have dramatically slowed breast cancer, but experts said the focus should now shift to changing behaviors like diet and physical activity.

"What can be achieved with screening has been achieved. We can't do much more," said Carlo La Vecchia, head of epidemiology at the University of Milan. "It's time to move on to other things."

La Vecchia spoke last month at a European breast cancer conference in Barcelona. He cited figures from the International Agency for Research on Cancer, which estimates that 25 to 30 percent of breast cancer cases could be avoided if women were thinner and exercised more. The agency is part of the World Health Organization.

His comments are in line with recent health advice that lifestyle changes in areas such as smoking, diet, exercise and sun exposure can play a significant role in risk for several cancers.

Dr. Olivia Aranha, an oncologist with Cape Medical Oncology, said studies have shown that exercise will help decrease cancer risk. She said it should be prescribed as a supplement to current screening practices.

"Prevention is an adjunct to screening mammograms to decrease the risk of breast cancer," she said. "Can exercise replace the need for mammograms? I don't think so at this time. I think it's an adjunct."

Aranha sees patients after they have had treatment for cancer. She said she prescribes the patient to get his or her heart rate above 100 for 30 to 45 minutes.

Exercise "ensures bone health and most breast cancers tend to come back in the bone if they come back," she said.

Dr. Michelle Holmes of Harvard University, who has studied cancer and lifestyle factors, said people might wrongly think their chances of getting cancer depend more on their genes than their lifestyle.

"The genes have been there for thousands of years, but if cancer rates are changing in a lifetime, that doesn't have much to do with genes," she said in a phone interview from Cambridge, Mass.

Breast cancer is the most common cancer in women. In Europe, there were about 421,000 new cases and nearly 90,000 deaths in 2008, the latest available figures. The United States last year saw more than 190,000 new cases and 40,000 deaths.

A woman's lifetime chance of getting breast cancer is about one in eight. Obese women are up to 60 percent more likely to develop any cancer than normal-weight women, according to a 2006 study by British researchers.

Many breast cancers are fueled by estrogen, a hormone produced in fat tissue. So experts suspect that the fatter a woman is, the more estrogen she's likely to produce, which could in turn fuel breast cancer. Even in slim women, experts believe exercise can help reduce the cancer risk by converting more fat into muscle.

Yet any discussion of weight and breast cancer is considered sensitive because some may misconstrue that as the medical establishment blaming women for their disease.

Tara Beaumont, a clinical nurse specialist at Breast Cancer Care, a British charity, said her agency has always been careful about giving lifestyle advice. She noted that three of the major risk factors for breast cancer -- gender, age and family history -- are clearly beyond anyone's control.

"It is incredibly difficult to isolate specific factors. Therefore women should in no way feel that they are responsible for developing breast cancer," she said.

Yet Karen Benn, a spokeswoman for Europa Donna, a patient-focused breast cancer group, said it was impossible to ignore the increasingly stronger links between lifestyle and breast cancer.

"If we know there are healthier choices, we can't not recommend them just because people might misinterpret the advice and feel guilty," she said. "If we are going to prevent breast cancer, then this message needs to get out, particularly to younger women."

That means avoiding becoming overweight as an adult. Robert Baan, a cancer expert with the international cancer research agency, said it isn't clear if women who lose weight can lower their risk to the level of a woman who was never fat.

The American Cancer Society website says the connection between weight and cancer risk is complex. It says risk appears to increase for women who gain weight as adults, but not for women who have been overweight since childhood. The cancer society recommends 45 to 60 minutes of physical activity five or more days a week to reduce the risk of breast cancer.

Drinking less alcohol might also help. Experts estimate that having more than a couple of drinks a day can boost the risk of breast cancer by 4 to 10 percent.

After studies several years ago linked hormone-replacement therapy to cancer, millions of women abandoned the treatment, leading to a sharp drop in breast cancer rates. Experts said a similar reduction might be seen if women ate healthier and exercised more.

Holmes, the Harvard expert, said changing diet and nutrition is arguably easier than tackling other breast cancer risk factors.

In the 1980s and 1990s, breast cancer rates steadily increased, paralleling a rise in obesity and the use of estrogen-containing hormones after menopause.

La Vecchia said countries like Italy and France -- where obesity rates have been stable for the past two decades -- show that weight can be controlled at a population level.

"It's hard to lose weight, but it's not impossible," he said. "The potential benefit of preventing cancer is worth it."

Features editor Chris Harris contributed to this report.