August 13, 2009
Cancer Mortality Rates Experienced Steady Decline
The number of cancer deaths has declined steadily in the last three decades. Although younger people have experienced the steepest declines, all age groups have shown some improvement, according to a recent report in Cancer Research, a journal of the American Association for Cancer Research.
"Our efforts against cancer, including prevention, early detection and better treatment, have resulted in profound gains, but these gains are often unappreciated by the public due to the way the data are usually reported," said Eric Kort, M.D., who completed the study while employed as a research scientist at Van Andel Research Institute (VARI) in Grand Rapids, Mich.
Cancer mortality rates are usually reported as composite age-adjusted rates. These rates have been declining modestly since the 1990's. However, these statistics heavily emphasize the experience of the oldest Americans for whom mortality rates are the highest. As a result, trends emerging in younger Americans can be concealed.
As an alternative to age-adjustment, Kort examined cancer mortality rates stratified by age and found that for individuals born since 1925, every age group has experienced a decline in cancer mortality. The youngest age groups have experienced the steepest decline at 25.9 percent per decade, but even the oldest groups have experienced a 6.8 percent per decade decline.
The public often hears about incidence rates, which continue to rise across many cancer types, or mortality proportions, with the World Health Organization's assertion that death from cancer will surpass death from heart disease by 2010. Both these calculations are accurate, Kort said, but they ask the wrong question. In particular, the often-quoted WHO statistic can be misleading.
Richard Severson, Ph.D., a cancer epidemiologist and associate chair of the Department of Family Medicine and Public Health Sciences at Wayne State University, said proportional mortality is calculated in groups of 100.
"When calculating proportional mortality, we start with the assumption that everyone dies of something eventually, so you take 100 deaths and calculate, based on death certificates, what those people have died from," said Severson, who reviewed the report for Cancer Research.
Cancer will surpass heart disease as a cause of death in 2010 because, while both heart disease and cancer have been declining, heart disease mortality rates have been declining much more rapidly. And while it's true that cancer incidence rates continue to grow, the decreased mortality across all age groups shows the effect of improved screening and treatment.
"In childhood cancer particularly, we're able to do amazing things with leukemia and lymphoma that used to be a death sentence but now we are curing many of these cancers," Severson said.
"This study focuses on an aspect that has been overlooked in determining whether we've had a significant impact on cancer mortality," said George Vande Woude, Ph.D., head of VARI's Laboratory of Molecular Oncology. Vande Woude helped conceive of the project and is one of the study's authors.
Vande Woude and Kort, currently a medical resident at Helen DeVos Children's Hospital in Grand Rapids, worked in collaboration on the project with Nigel Paneth, M.D., of Michigan State University's College of Human Medicine, departments of Epidemiology and Pediatrics and Human Development. The project was funded by a grant from the National Institute of Child Health and Human Development and Van Andel Institute.
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