September 5, 2012 (Montreal, Quebec) — More than 50% of cancer could be prevented if people simply implemented what is already known about cancer prevention, according to a researcher here at the Union for International Cancer Control (UICC) World Cancer Congress 2012.
Graham Colditz, PD, DrPH, from the Washington University School of Medicine in St. Louis, Missouri, reported that a number of interventions, largely involving lifestyle behaviors, but also involving higher-cost interventions in high-income countries, could prevent a large proportion of cancers in 15 to 20 years if widely applied.
Among the “biggest buys” from lifestyle intervention is smoking cessation.
“One third of cancer in high-income countries is caused by smoking,” Dr. Colditz said. If smoking rates could be reduced to the current levels in Utah [about 11%], the United States could see a 75% reduction in smoking-related cancers in 10 to 20 years — a target that Dr. Colditz feels is feasible in countries where smoking rates have already declined considerably.
Similarly, it is estimated that being overweight or obese causes approximately 20% of cancer today. If people could maintain a healthy body mass index (BMI), the incidence of cancer could be reduced by approximately 50% in 2 to 20 years. (A healthy BMI for cancer prevention is from 21 to 23 kg/m², as other speakers pointed out.)
Dr. Colditz, among others, estimates that poor diet and lack of exercise are each associated with about 5% of all cancers. Improvement in diet could reduce cancer incidence by 50% and increases in physical activity could reduce cancer incidence by as much as 85% in 5 to 20 years.
Eradicating the main viruses associated with cancer worldwide by implementing widespread infant and childhood immunization programs targeting 3 viruses — human papillomavirus and hepatitis B and C — could lead to a 100% reduction in viral-related cancer incidence in 20 to 40 years, he added. Then there are the “higher tech” interventions that, at least in high-income countries, could prevent a significant proportion of cancer and cancer-related mortality, starting with breast cancer.
“We have shown that tamoxifen reduces the rate of both invasive and noninvasive breast cancer by 50% or more, compared with placebo, at 5 years,” Dr. Colditz said.
Similarly, raloxifene has been shown to reduce the risk for invasive breast cancer by about 50% at 5 years, according to the Study of Tamoxifen and Raloxifene (STAR) in postmenopausal women at increased risk for breast cancer. Women in STAR who received raloxifene also had 36% less uterine cancers than control subjects.
“We also observed a 10% to 15% decrease in breast cancer incidence following the results of the Women’s Health Initiative that were clearly not due to changes in mammography, but rather to the removal of a late promoter [of breast cancer],” Dr. Colditz explained. The use of hormone replacement therapy in the United States plummeted after the Women’s Health Initiative showed that it was associated with an increased risk for breast cancer.
And bilateral oophorectomy in women carrying the BRCA1 or BRCA2 gene, although rare, has been associated with a 50% reduction in breast cancer risk among high-risk women. It has also been estimated that weight loss after menopause (more than 20 lbs [9 kg]) reduces breast cancer risk by 50% in 2 to 20 years.
In addition, Dr. Colditz noted that approximately 20 years of follow-up has shown that aspirin is associated with a 40% reduction in mortality from colon cancer. Screening for colorectal cancer has a similar magnitude of mortality reduction (30% to 40%).
Indeed, a recent study showed that after a median follow-up of 11.9 years, there was a 21% relative risk reduction in the incidence of colorectal cancer and a 26% reduction in mortality in adults screened with flexible sigmoidoscopy, with a repeat screening at 3 or 5 years, compared with those treated with the usual care (N Engl J Med. 2012;366:2345-2357).
Dr. Colditz noted that a concerted and collective effort to promote colon cancer screening in Massachusetts was initiated in 1997. From 1997 to 2010, “we saw almost a doubling of screening with sigmoidoscopy or colonoscopy in age-eligible residents and, during that time, the age-standardized mortality from colon cancer went down by 35%,” he said.