New cases of cancer among adults in California are declining, but rates of childhood cancers are increasing, according to a new study by a statewide health organization.
The report, by the California HealthCare Foundation, also shows that cancer survival rates are improving for kids and adults.
Researchers and oncologists point to several trends, such as falling smoking rates, that explain the declines in new adult cancer cases in the last 20 years. But for childhood cancers, massive studies are under way, and available explanations don’t offer a complete picture of why more kids are getting sick.
Since 1989, the rate of new cancers in California adults has fallen from 456 per 100,000 residents to 413, about a 9 percent decline, according to the foundation report, released last week. Rates among children inched up, though, from 15.4 cases per 100,000 children to 17.8, an increase of about 15.6 percent.
The decline in adult cancer cases has been driven by successful efforts to cut the smoking rate in California, which led to a drop in lung cancer rates, said Tina Clarke Dur, an epidemiologist with the Cancer Prevention Institute of California. She also said there was a 15 percent drop in breast cancer cases soon after women learned about the dangers of hormone replacement therapy in 2003.
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As for the gradual rise in childhood cancer cases, most of which are leukemia, the answers are not as clear.
Dr. Catherine Metayer, a UC Berkeley epidemiologist who studies the causes of childhood cancer, said researchers all over the world are collaborating to find answers for why children get leukemia. She said leukemia, or cancer of the blood, accounts for about 35 percent of childhood cancers, with brain tumors coming in second.
Metayer said researchers have known for about 15 years that Down syndrome and exposure to radiation are risk factors. They currently suspect that a combination of genetic and environmental causes lead to childhood leukemia, but neither is fully understood.
However, she said scientists are focusing on risks presented by the use of household pesticides during pregnancy and when children are young. She said researchers in several countries have found that families have nearly twice the risk of having a child with leukemia if they used a product to kill ants, rats, fleas or other pests.
Metayer said emerging research is showing a slight increase in leukemia risk if a father smoked before a baby was conceived. Higher rates of chemicals called PCBs, which are very common, also are linked with higher rates of leukemia, she said. And scientists have linked higher birth weight to slightly higher leukemia risks, but don’t fully understand why.
“We are starting to get clues to what can cause leukemia, but I think we’re at the early stage of fully understanding the causes,” Metayer said.
Ongoing studies are examining genetic factors, immune system development and chemicals found in household dust, she said.
For both children and adults, though, cancer survival rates improved from 1989 to 2009. For adults, mortality rates fell by 22 percent, with 158 per 100,000 people dying of cancer in 2009. Mortality fell just as much for kids, with a 21.6 percent decline through 2008.
Dr. Jonathan M. Ducore, a cancer epidemiologist and pediatric oncologist at UC Davis Medical Center, said physicians have gotten better at treating childhood cancers.
He said oncologists treating leukemia have learned that intensive treatment regimens improve survival rates. “Part of it is kids, pound for pound, are tougher than adults, and we can treat them much more aggressively than adults,” Ducore said.
Ducore said that in addition to kids healing faster and being more resilient than adults, stepped-up treatments are effective at eliminating leukemia.
As for the increase in childhood cancer cases, Ducore said research has pointed to small increases in risk. But no discovery about childhood cancer has been as significant as those linking smoking to lung cancer.
“For the causes,” he said, “it’s a big question mark.”
Editor's Note: Due to inaccurate data reported by the California HealthCare Foundation, an earlier version of this story misstated childhood cancer incidence and mortality rates. The number of new cases per 100,000 children was 17.8 in 2008, an increase of 15.6 percent from 1989 to 2008. Childhood mortality rates decreased 21.6 percent from 1989 to 2008. The mortality rate was 2.9 deaths per 100,000 children in 2008.