What is DIPG?
Diffuse intrinsic pontine glioma (DIPG) is a brain tumor found in a part of the brain stem called the pons. The pons controls essential bodily functions such as heartbeat, breathing, swallowing, eye movement, eyesight, and balance.
DIPG affects children almost exclusively. Approximately 200-400 children in the United States are diagnosed with DIPG each year. These children are typically between the ages of 4 and 11. DIPG accounts for roughly 10-15% of all brain tumors in children.
DIPG is an aggressive tumor that interferes with all bodily functions, depriving a child of the ability to move, to communicate, and even to eat and drink.
As a DIPG tumor begins to grow, it puts pressure on the nerves that control the essential bodily functions regulated by the pons. Children with DIPG commonly experience double vision, reduced eye movement, facial weakness or asymmetry, and arm and leg weakness. They also have problems with walking, coordination, speech, chewing, and swallowing. As the tumor progresses, it also interferes with breathing and heartbeat, which ultimately results in the child’s death.
What causes DIPG?
No one knows what causes a child to develop a DIPG tumor. Some cancers are caused by particular genes that a person inherited from their parents, but there is no evidence that links DIPG to any specific inherited genes. Other cancers are caused by environmental factors (such as smoking or exposure to chemicals or radiation), but there is no evidence that links DIPG to any environmental factor.
Recent research has suggested that DIPG tumor formation may be linked to brain development. These studies suggest that the disease process may be influenced by particular cells that are present in the highest concentrations while the brain is developing. The theory that DIPG is linked to brain development is also supported by the fact that DIPG most often occurs during middle childhood (ages 5-10), a period in which the brain develops significantly. It would also explain why adults do not commonly get DIPG tumors.
Recent research has also identified genetic and epigenetic mutations that are present in DIPG tumors. But more research is needed to determine which of these mutations cause the DIPG tumor to form, and how they do that. And more research is needed to determine what causes the mutations to occur in the first place.
What is the treatment?
Unlike many brain tumors, a DIPG tumor cannot be removed through surgery. Attempting surgical removal of a brain stem tumor would likely cause severe neurological damage and could even be fatal.
Surgery is not an option for two reasons. First, because the pons is located in the center of the brain, a surgeon could not get to the tumor without damaging the surrounding portions of the brain. Second, even if the tumor could be accessed, total removal would be impossible. A DIPG tumor is not a solid, well-defined mass like some tumors. Instead, the tumor cells spread out between the healthy brain cells. Because the tumor cells could not be entirely removed without also removing the healthy cells, even if surgery were performed, the remaining cells would continue to divide and the tumor would soon return.
A biopsy is a sample of tissue removed from the body for testing. For many tumors, a biopsy is a standard diagnostic tool because it allows the doctors to determine the tumor’s precise characteristics.
Until a few years ago, doctors did not perform a biopsy to diagnose DIPG. They instead diagnosed the disease based solely on a patient’s symptoms and MRI scans. Doctors have not traditionally performed biopsies for two reasons: (1) the risk of causing serious neurological damage was high, and (2) there was little benefit to doing the procedure because the results of the biopsy did not affect how the patient would be treated.
Biopsies are common today. The risk that a biopsy will cause neurological damage has been greatly reduced as a result of recent technological advances. As part of a surgical procedure known as a “stereotactic” biopsy, a computer relies on MRI scans of the child’s brain and tumor to guide a thin needle into the tumor to extract cells, while avoiding the critical nerves that run through the pons.Given their increased safety, stereotactic biopsies are becoming part of the standard care for DIPG patients. Recent research has shown that not all DIPG tumors are the same. New clinical studies are attempting to personalize the course of treatment for each DIPG patient based on the particular characteristics of each patient’s tumor. Those characteristics can be determined only by performing a biopsy.
The increase in biopsies has been a critical factor in the development of our understanding of the biology of DIPG tumors.
Radiation is part of the standard course of treatment for DIPG patients, as it is the only form of treatment that has proven benefits. For roughly 70% of DIPG patients, radiation causes the tumor to shrink, which provides relief from many of the symptoms associated with DIPG.
The benefits of radiation, however, are usually only temporary. Even for those patients whose tumors shrink during radiation, the tumor begins to grow again within months. Because DIPG patients who do not undergo radiation have a median survival length of roughly 5 months, radiation therapy typically extends a patient’s life by about 3 months.
Proton radiation therapy has become popular in recent years for many types of cancer, but most doctors and radiologists do not see a benefit in using this treatment for DIPG tumors. Proton radiation therapy’s primary benefit is that it relies on a proton beam that is more precise than the electron beam used in traditional radiation. This benefit is valuable for solid, well-defined tumors because it allows the radiologist to attack the tumor while sparing the surrounding, healthy cells. This extra precision is not beneficial for DIPG, however. Because a DIPG tumor does not have well-defined edges — the tumor cells spread through the pons, intertwining with the healthy cells — radiation cannot be limited to the solid mass, but instead must extend to the areas around the tumor.
Numerous clinical studies have attempted to improve the effectiveness of radiation by combining radiation with radiosensitizers, which are drugs intended to make cancer cells more likely to die from the radiation. None of the studies so far have shown any benefit to adding a radiosensitizer.
In the past 30 years, DIPG patients have participated in more than 250 clinical trials. These trials have involved a wide array of chemotherapy drugs – sometimes alone and sometimes in combination with other drugs. None of these studies have shown any benefit in either the likelihood of survival or the median length of survival.
Doctors and researchers are actively searching for effective chemotherapy agents. Given the increased understanding of the biology of DIPG tumors, these new approaches can be tailored to the particular characteristics of the DIPG tumor in ways that prior trials could not. These recent developments have given doctors and researchers reasons to be optimistic that they will develop effective treatments for DIPG in the future.
What is the prognosis?
Medical advances in the past 40 years have greatly improved the survival rates for children diagnosed with most types of cancer. For some cancers, the medical advances have been extraordinary. For example, the survival rate for children with acute lymphocytic leukemia has increased from less than 10% in the 1960s to nearly 90% today. Overall, the survival rate for children with cancer is around 83%.
But these medical advances have done nothing for children with DIPG. Brain tumors remain the most common cause of cancer-related death in children, and DIPG is the leading cause of death from pediatric brain tumors. A child diagnosed with DIPG today faces the same prognosis as a child diagnosed 40 years ago. There is still no effective treatment and no chance of survival. Only 10% of children with DIPG survive for 2 years following their diagnosis, and less than 1% survive for 5 years. The median survival time is 9 months from diagnosis.