Pediatric Brain Tumor Research: Unique Challenges and Opportunities

Just as children are not miniature adults, pediatric cancers aren't small adult cancers. The distinct biology of pediatric brain cancer means it often needs different treatment and can also give us insights into the origins and cures to all cancers
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At the age of 10, my friend Sydney was diagnosed with a tumor in her brainstem, the part of the brain that controls life's most vital functions. Her cancer was inoperable and did not respond to other treatments. Sydney, the most vivacious member of my fifth grade class, had her life taken by this unforgiving disease when she was only 11 years old.

Pediatric brain cancer touches people's lives in a unique way. "When a tumor grows in the brain it threatens to affect the core of the self," said Dr. Sarah Leary, a physician at Seattle Children's Hospital. "The brain is the center of who we are, and it can't be removed and replaced." Couple this integral location with the fact that it's a cancer arising in children, and it's even more disturbing. The apparent randomness in the incidence of pediatric brain cancers clashes with our sense of justice and fairness. While we can look to an aging smoker who develops lung cancer and point to a lifetime of inhaling carcinogens as a causal factor, no such rationale exists with pediatric cancers. However, promising research focused specifically on pediatrics may be the key to unlocking cancer's mysteries.

Most cancer research is focused on adults, who make up 92 percent of brain tumor diagnoses annually. But the other 8 percent of brain cancers -- the 2,284 kids like Sydney who get this disease each year -- hold a significance that is not conveyed by their relatively small representation. Just as children are not miniature adults, pediatric cancers aren't small adult cancers. The distinct biology of pediatric brain cancer means it often needs different treatment and can also give us insights into the origins and cures to all cancers. In fact, in the 1960s, it was childhood acute leukemia that showed that combination chemotherapy was an effective cancer treatment. With some advancements, this remains the standard of care in many cancers.

Key differences
For reasons we do not yet fully understand, possibly due to their rapidly-developing brains, cancers in children are far more likely to be in the brain than adult cancers are. While brain cancer is the second most common pediatric cancer, it doesn't even make the top 10 list in adults.

The nature of the many different cancers and the developing brain make treatment options different for children than for adults. Pediatric cancers are more likely to be in high-stakes regions of the brain that control vital life functions, making them harder to operate on. Sydney's cancer couldn't be operated on because it invaded through her brainstem, rendering surgery impossible. Radiation therapy can also be too risky for young children. Since their brains are still rapidly growing and developing, the damage that radiation does to healthy DNA can be too devastating to be worthwhile. In treating pediatric brain cancer, doctors have to make hard decisions about whether a therapy will do more harm than good.

Though pediatric cancers often need inherently different treatments than adult cancers, they are often regarded as miniature adult cancers in the drug trial and approval process. "It is quite common that pediatric trials are only initiated after a trial has been successful in adults," said Dr. Michelle Cook Sangar of the Fred Hutchinson Cancer Research Center. "And, if an adult clinical trial is cancelled due to lack of efficacy then a pediatric trial will likely not be conducted," meaning that many treatments that could've been effective in children are never given the chance.

Treatment of pediatric brain cancer is more likely to include intensive chemotherapy, with increased short-term side effects as a trade-off for better long-term outcome if radiation can be reduced or avoided. It has been seen that children actually tolerate these intense therapies relatively well, often still participating in school and sports during treatment that would leave older adults bedridden. Months into her treatment, Sydney was able to attend summer camp and perform in a play.

According to the American Cancer Society, children across brain cancer types have a 75 percent five-year survival rate. However, the lasting side effects of brain tumors and treatments are often more pronounced for children who had cancer in their brains than other childhood cancers. Long-term side effects such as learning disabilities, hormonal imbalances, vision problems, trouble balancing, fertility problems, and hearing loss remain in most pediatric brain cancer survivors. Many young patients will also face recurrence in their lifetimes.

Unique insights
The differences in manifestations and treatments of brain cancer in children and adults are mainly rooted in their different genetic origins. Pediatric cancers are generally caused by a few key genetic changes, while adult cancers may have large numbers of changes accumulated over a lifetime and influenced by environmental factors. Looking at childhood cancer can give us a clearer lens into cancer's origins.

At the Brain Tumor Immunotherapy Program at the University of Florida, Dr. Duane Mitchell is tapping into the unique insights into the immune system that pediatric cases can give us. His work in genetic immunotherapy uses mechanisms that already exist in our body to fight cancer based on an individual patient's genome. (Mitchell, Duane. Personal interview. 12 September 2014.)

After a patient undergoes chemotherapy, the body works to re-build its immune system, creating the perfect opportunity to administer immunotherapy. The more chemotherapy a patient has been given, the better immunotherapy can work. Children's tolerance of chemotherapy makes them excellent candidates for Dr. Mitchell's research. (Mitchell, Duane. Personal interview. 12 September 2014.)

The immune system has an exceptional memory, meaning that immunotherapies could prevent cancer from recurring. Immunotherapy has fewer long-term side effects relative to the current standards of surgery, radiation, and chemotherapy. Early trials of targeted immunotherapy in both children and adults have demonstrated the safety of the approach and prevented tumor regrowth in several patients for periods extending beyond two years. (Mitchell, Duane. Personal interview. 12 September 2014.)

Moving Forward
Because of the promise found in early trials, Dr. Mitchell's immunotherapy is moving into more extensive trials in pediatric brain cancer patients nationwide. Someday the lessons we've learned from these trials may help us to mobilize all patients' immune systems against their cancers.

It is integral that we emphasize not only the heartbreak of pediatric cancer, but the immense value of great pediatric cancer research. As leaders in the fight against brain cancer in my positions at both Accelerate Brain Cancer Cure and the Pink Polka Dots Guild, we recognize the importance of pediatric cancer research in accomplishing our goal of finding a cure, as well as in helping children like Sydney live their lives to the fullest.

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