Increase in childhood cancer a puzzle

June 21, 2012

By Elise Craig
California Health Report

The rate of new cases of children’s cancer is on the rise in California and the reasons for the increase are difficult to determine.

While cases of cancer among adults in the state have dropped by about 9 percent over the last 20 years, the children’s cancer rate has increased by about 16 percent in that same period, according to a report released last week by the California Healthcare Foundation.

The contributing factors for the decrease in cancers for adults are fairly simple to pinpoint. “Clearly the success of the smoking cessation efforts here have much to do with the decline,” said Tina Clarke Dur, an epidemiologist and research scientist at the Cancer Prevention Institute of California.

“We also saw a major decline in breast cancer, the most common cancer diagnosed in women in 2003 after older women largely stopped taking hormone replacement therapies.”

The rate of lung cancer in particular is dropping more rapidly than other cancers in California, and more rapidly here than in other states, Clarke Dur said.

But the possible drivers of the bump in the rate of children’s cancers are more elusive.

“We don’t really know why pediatric cancer happens,” said Dr. Anjali Pawar, a pediatric oncologist at the UC Davis Medical Center.

Leukemia accounts for about one third of children’s cancers, and leukemia and cancers of the brain and central nervous system make up more than half, according to the National Cancer Institute.

Though studies have linked leukemia to radiation exposure, pesticide use and genetic conditions like Down syndrome, scientists don’t have a full understanding of the causes of these diseases, or how environmental factors interact with genetic factors.

Risk factors for these cancers have been far more difficult to pinpoint than cancers that commonly affect adults, like lung or bladder cancer, which have been linked to smoking, or breast cancer, which has been linked to hormone therapy and other factors.

Part of it, too, is that from a broad perspective, few children actually get cancer, so the pool of cases to study from is comparatively small. Nationally, fewer than 13,000 new children’s cancer cases are diagnosed every year. In comparison, more than 230,000 people were diagnosed with invasive breast cancer alone in 2011.

Though 95 percent of children who are treated for cancer have some of their material—blood or tumor samples, for example—stored for further study, it’s still a far smaller set of sheer data to draw from than adult cancers, Dr. Pawar said.

But in terms of finding drivers for the increase in the cancer rate among children,

“The most important clues would be those linked to leukemia,” Clarke-Dur said.

However, recent evidence has tied childhood leukemia to overuse of pesticides.

“Pesticides have definitely come into focus as a driver of the increase in cancers, especially in children, but how exactly they might contribute at the cell level, they’re still working on it,” Dr. Pawar said.

Studies have also shown that mothers who did not take folic acid supplements during pregnancy are more likely to have children who develop cancer.

But the news isn’t all bad. The rate of some children’s cancers like Hodgkin’s has dropped, and in that same 20-year period, the mortality rate for childhood cancers in the state has fallen by about 22 percent.

Treatment of children with leukemia has been very successful, and children who are treated for leukemia have a 95 percent chance of event-free survival within the first five years, and an 85 percent chance for the first ten, Pawar said.

“We have achieved the maximum amount of survivors we can for children with leukemia,” she said. “What we need now are better drugs which can be targeted to individuals.”

One of the problems with treating children’s cancers is exposing them to chemotherapy and radiation that can cause other health problems, including therapy-related cancers, down the line. Individualized medicine and gene therapy could help reduce the risks of other illnesses later in life.

“More funding would be good,” Pawar said. “Research for pediatric oncologists is very important. We have smaller numbers, and our patients don’t vote.”

Though doctors can’t say definitively what’s causing childhood cancers, they still have tips for prevention.

“Stop smoking—by far and away best cancer preventive step we know—keep your weight down, improve your diet and physical activity, avoid getting yourself or your children in particular sunburned,” Clarke Dur said.

And though most people think of weight as a risk factor for diseases like diabetes and heart disease, it’s a risk factor for cancer survival as well.

“There’s nothing like aerobic physical activity,” Pawar said. “It helps you build up your immune system. If you have a healthy immune system, most of the tumor cells are nipped in the bud. And even if do get it, you withstand the therapy better.”

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