Environmental Factors the Major Cause of Cancer
BETHESDA, Maryland, June 28, 2004 (ENS) - Most cases of cancer are linked to environmental causes, U.S. government scientists report, and simultaneously, a second group of government researchers says the number of cancer survivors is growing in the United States. Cancer is the second leading cause of death for Americans after heart disease.
But more people diagnosed with cancer are living longer today than ever before. A new report by the Centers for Disease Control and Prevention (CDC) and the National Cancer Institute (NCI) released Friday shows that 64 percent of adults whose cancer is diagnosed today can expect to be living in five years.
The majority, 61 percent, of cancer survivors are aged 65 and older, and the study estimates that one of every six people over age 65 is a cancer survivor. The findings are published in the June 25 issue of CDC’s Morbidity and Mortality Weekly Report, “Cancer Survivorship – United States, 1971 – 2001.”
Cancers linked to environmental causes make up at least 80 percent of all cancer cases, according to a second new report by the National Cancer Institute, this one published with the National Institute of Environmental Health Sciences. Environmental causes include exposure to agents in the air and water as well as lifestyle factors such as smoking and diet.
"Most epidemiologists and cancer researchers would agree that the relative contribution from the environment toward cancer risk is about 80-90 percent," said Aaron Blair, Ph.D., the chief of the Occupational Epidemiology Branch in NCI's Division of Cancer Epidemiology and Genetics. "There is very solid evidence that environmental factors are the major cause of cancer," he said.
Evidence comes from studies of people who migrate from an area of high cancer risk to an area of low cancer risk, or the reverse, Dr. Blair said. They invariably take on the cancer rates of the country to which they move.
"Since the gene pool changes only after many generations, this means that these changes must be environmental, not genetic," said Dr. Blair. "And so, the migrant studies very clearly tell us that the wide range of cancer rates is largely driven by environmental causes."
For decades, Dr. Blair said, scientists have been conducting epidemiological investigations of the causes and distribution of cancers, looking at a variety of environmental and host genetic risk factors. "Almost always," he said, "the cancer burden is much greater for environmental causes than just the hereditable genetic factors."
Whatever the cause, people in the United States who have been diagnosed with cancer are living longer. Today, there are 9.8 million cancer survivors across the country.
"Being a cancer survivor is at the forefront of my self awareness," says 80 year old Mortimer Brown of Florida, a colorectal cancer survivor diagnosed at age 75. "It enters into the conversations that I have with myself about what I want to do, how I want to spend money, how I want to spend time, my energy, all of that. Being a cancer survivor has added another dimension to my identity. I am a cancer survivor.”
Health and Human Services Secretary Tommy Thompson said Friday, "The number of cancer survivors in this country has increased steadily over the past 30 years for all cancers combined. We expect the number of survivors to increase as improvements are made in cancer detection, treatment and care and as the population ages."
The authors of the survivorship study used incidence and follow-up data from NCI’s Surveillance, Epidemiology and End Results (SEER) program to estimate annual cancer prevalence – the number of people living following a diagnosis of cancer – and trends in cancer survivorship.
Breast cancer survivors make up the largest group of cancer survivors, 22 percent, followed by prostate cancer survivors (17 percent) and colorectal cancer survivors, 11 percent.
Seventy-nine percent of childhood cancer survivors will be living five years after diagnosis and nearly 75 percent will be living 10 years following diagnosis, the CDC and NCI study found.
CDC’s Division of Cancer Prevention and Control is supporting states, tribes and tribal organizations to develop and incorporate survivorship priorities into their comprehensive cancer control plans.
"There is a growing need to promote health and ensure the social, psychological and economic wellbeing of cancer survivors and their families," Dr. Pollack said.
CDC is also working with national organizations to promote education, awareness and community programs that offer services and support for cancer survivors.
“My concerns as a survivor have evolved the farther away I have gotten from treatment," says 24 year old Karen Dyer of New York, who was diagnosed with rhabdomyosarcoma at age 15.
"During my treatment and for several years after…my primary concern was recurrence and, although I haven’t had any, I would be lying if I say that I don’t think about it all the time. [Now] I worry about secondary cancers," she told the President's Cancer Panel for its 2003-2004 Annual Report "Living Beyond Cancer: Finding a New Balance."
To prolong life for cancer survivors, avoiding further exposure to cancer causing factors is critical. Dr. Blair says the specific environmental factors involved differ by tumor.
Tobacco smoke is the major cause of lung cancer, he says, "But there is a long list of other chemicals that cause lung cancer - arsenic, asbestos, PAHs (polyaromatic hydrocarbons), and chromium, to name a few."
"For breast cancer, hormone use is one of the major factors affecting risk. Prostate cancer has nothing that reaches the level of evidence of lung or breast cancer, although there are a number of strong leads. Physical inactivity is strongly linked to colorectal cancer, as well as a number of dietary factors - low fiber is probably implicated," said Dr. Blair.
Tobacco as a cause of cancer is easy to study, Dr. Blair says, because it is a single agent. Diet and environmental pollutants are more difficult, he said.
"The major limitation is that it is so difficult to characterize a person's diet over time," he said. "Typically it's not the diet today that is important for the cancer diagnosed today. We need to know what people ate in the past, and that is really hard to determine."
Environmental pollutants are linked to the incidence of cancer and its recurrance, although this field is also difficult to study, said Dr. Blair. "Researchers are beginning to focus on potentially hazardous substances in the water and air," he said. "This is a difficult research area and is every bit as hard to study as diet."
In response to the growing number of cancer survivors in the United States, many organizations are involved in survivorship issues, particularly the group founded in 1997 by cancer survivor and champion cyclist Lance Armstrong.
"This award celebrates young people in our communities who have overcome tremendous challenges and whose energy and dedication inspire others," said Betsy Goldberg, survivorship associate for the Foundation. "The Junior Spirit of Survivorship Award demonstrates that anyone - even young people - can be an effective advocate and a hero for other cancer survivors."
The Junior Spirit of Survivorship Award winner will join the ranks of the recipients of the prestigious Carpe Diem Awards, which recognize individuals who have made a significant contribution to the world of cancer survivorship.
The CDC and the Lance Armstrong Foundation have published a National Plan for Cancer Survivorship: Advancing Public Health Strategies. Young people particularly need this kind of help.
“I was going through treatments at the age of, essentially, 13 to 18, the developmental years in my life," says 30 year old Sean Swarner of Colorado, who was diagnosed with Hodgkin’s lymphoma and primitive neuroectodermal tumor (Askin’s disease) at age 13. "I really didn’t understand the impact of what I went through until after I went through college and went for my master’s degree…when I re?ected on my life and realized that what I went through didn’t make me who I am, but it had an incredible impact on my life."
"I think it would have helped to actually have some type of, not necessarily support group, but literature, the Internet, anything to provide [information on] those long-term psychological effects,” he said.
“Issues faced by cancer survivors include maintaining optimal physical and mental health, preventing disability and late-effects related to cancer and its treatment, and ensuring social and economic well-being for themselves and their family,” said Dr. Julia Rowland, director of the Office of Cancer Survivorship at NCI.
“NCI takes these factors into consideration when conducting research to identify, examine and prevent or control adverse effects associated with cancer," she said. "We are working to enhance survivors’ quality of life.”