Despite dramatic improvements in the survival rate of cancer patients, a recent government report shows that the number of new cases continues to rise--and experts can't explain why.
"We have been worried about increases in the incidence of cancer for a long time," says Dr. Edward J. Sondik, deputy director of the National Cancer Institute's (NCI) Division of Cancer Prevention and Control, which issued the sobering report. "But we have to be careful about setting off alarms until there (is) data" that supports action.
From 1973 to 1987, the overall age-adjusted incidence of cancer (new cases per 100,000 people per year) rose 15%, according to NCI statistics. Cancer cases have risen among blacks, whites, men, women and most age groups, including children.
For white children 14 and younger, new cases of leukemia and brain cancer have risen about 30% in only 15 years. Overall, the incidence of childhood cancer rose 6% in that time.
"The sad truth is we don't really know what's causing a lot of these changes," explains Dr. Devra Davis, a professor of occupational and environmental medicine at Mt. Sinai Medical School in New York City. Davis, the author of a separate study that found cancer increases in six other industrialized Western nations, believes that the causes for most of the increases fit into two categories: cancer-causing chemicals and lifestyle.
"I wouldn't be surprised if some as yet unrecognized aspect of modern industrial life was involved," says Davis, citing asbestos, agricultural pesticides and industrial solvents as possible causes.
Dr. Emily White, an epidemiologist at the Fred Hutchinson Cancer Research Center in Seattle, believes that lifestyle plays a far more important role than chemicals in causing cancer. "I know of almost no evidence that environmental toxins cause the increases," she says, and instead emphasizes lifestyle factors such as smoking, high-fat diets, excessive drinking and sunbathing.
The largest rise for any cancer from 1973 to 1987 was for melanoma, the deadly skin cancer, which increased by 83%. This sharp rise is strongly linked to sun exposure.
In tracking long-term cancer trends, the report produced its most spectacular finding: a nearly 500% increase in female lung-cancer cases since 1950. "That statistic ought to throw people back on their heels," Sondik says. (Lung cancer cases among all adults rose 32% during that time.)
The reason for the surge among women comes as no surprise: They've taken up cigarette smoking in record numbers over the past 40 years. As a result, lung cancer has now surpassed breast cancer as their leading cause of cancer deaths.
Breast cancer is also on the rise, up 23% between 1973 and 1987.
Cervical cancer stands as a bright spot in the generally gloomy report. The incidence fell 36%, which Sondik attributes to increased use of Pap smears.
The survey noted a significant long-term decline in stomach cancer, with new cases decreasing 73% since 1950. "What's absolutely fascinating," Sondik says, "is if you look at statistics for several countries, you see stomach cancer falling, even in Japan and the United States, where the rate is high. Unfortunately, nobody knows why."