It is truly an exciting time in cancer discovery. Discoveries in cancer genetics, immunology, and cancer stem cells are leading us to new, personalized therapies that target the specific cells and cellular alterations that drive the cancer. For children, this represents a huge step forward, as this new generation of treatments will not be as toxic to healthy tissue and cells, and, therefore, may spare young patients the lasting side effects that often result from cancer treatment. These discoveries also offer new opportunities to better understand and make real progress against those pediatric cancers that do not respond to existing treatments.
Pediatric Cancer Research Advances of 2010
BREAKING NEWS – First Pediatric Cancer Genome Mapped
Johns Hopkins Kimmel Cancer Center researchers have led the world in mapping the genetic blueprints of several common adult cancers, and now, our scientists have become the first to decipher the genetic code of a pediatric cancer. Their findings were reported in the December 16, 2010, issue of the journal Science. Using sophisticated new gene sequencing technologies, the team mapped the genetic sequence of medulloblastoma, the most common type of pediatric brain cancer. As suspected, this analysis clearly shows that genetic changes in pediatric cancers are remarkably different from adult tumors. The work revealed fewer genetic alterations than are typically found in adult tumors, and the researchers believe this may make it easier to use the findings to develop new therapies. The research also uncovered epigenetic alterations, biochemical variations that occur to the environment of genes and have the ability to turn genes on and off without mutating them, as a more significant culprit in pediatric cancer than commonly thought. Using drugs to block the abnormal biochemical activity can return normal gene function and stop the development of cancer cells. Information like this, gained from gene sequencing technology, could potentially help our team change the course of some relentless childhood cancers. As a result, we hope to continue this work in other pediatric cancers.
Dr. Patrick Brown is developing desperately-needed new clinical approaches for infant acute lymphocytic leukemia (ALL). Currently, with just 20 to 40 percent of patients surviving, it has the most dismal survival rates of any form of childhood leukemia. Dr. Brown suspects that alterations to the FLT3 gene, which was indentified and cloned by Dr. Donald Small, may be allowing the cancer to evade treatment. He is currently leading a national study of 50 patients to test a FLT3 inhibitor. By blocking FLT3, Brown and team are hopeful that the cancer will respond to chemotherapy. Earlier studies showed that the drug successfully turns the gene off, and ongoing studies will confirm if it making a difference in treatment responses.
He is also studying a FLT3 inhibitor in children with acute myeloid leukemia (AML) who have relapsed after chemotherapy. About 20 percent of children with AML have FLT3 mutations, and Brown believes it is a key reason their cancers often return after treatment. Another related study will test the FLT3 inhibitor treatment as the first line of therapy.
In the laboratory, researchers Drs. Mark Levis and Keith Pratz are working on the next generation of FLT3 inhibitors. The new drugs are more potent and selective for FLT3. They will be the focus of a collaborative study of pediatric leukemia patients at the Kimmel Cancer Center and 13 other national cancer centers, known for their expertise in leukemia.
Dr. Brown’s goal is make FLT3 inhibitors and chemotherapy effective enough to get all patients into a lasting remission so that they can undergo bone marrow transplant, but ultimately, with continued research, he hopes that FLT3 inhibitors and chemotherapy will cure patients so that they will not require a transplant.
Treatment for pediatric sarcomas has not changed much since the 1980s. Future advances in the care of children with sarcoma will only come from a deeper understanding of the biology of these tumors, and the translation of this understanding into clinical trials.
Dr. David Loeb, M.D., Ph.D., Director of the Musculoskeletal Tumor Program, is working to drive this progress.
An exciting new area of research is in cancer stem cells. These cells represent a rare and stealth population of cells that often escapes the assault of anticancer drugs and drive the growth of tumors. Like the typical stem cell that helps form and regenerate tissue and cells, cancer stem cells are capable of limitless growth, self-renewal, and the generation of new tumors.
In Ewing’s sarcoma, one of the most common bone tumors among adolescents, patients often go into remission, but the cancer almost always returns, resulting in a dismal long term survival rate of just 10 percent. Researchers have long noted a discord between initial good responses to chemotherapy and ultimate chance of survival. The Johns Hopkins team suspects that while chemotherapy destroys the bulk of the tumor, it does not get at the cancer stem cells. These resistant cells then eventually drive the growth of tumor cells, causing the cancer to return.
Ongoing work is now focused on identifying the Ewing’s sarcoma cancer stem cell. One study is examining whether using drugs that interfere with the metabolism of cancer stem cells could kill them. Another therapy that targets a specific enzyme is being studied for its potential to kill Ewing’s sarcoma and rhabdoymosarcoma cancer stem cells. With promising early laboratory data, the team is working to move quickly to clinical trials of the drug.
Finally, researchers are studying a drug, arsenic trioxide, currently used to treat leukemia that may be toxic to the cancer stem cells. Since the drug is already FDA approved, clinical trials can be rapidly initiated.
Bone Marrow Transplantation:
For pediatric patients who need bone marrow transplants (BMT) to be cured, Drs. Allen Chen and Heather Symons are working to make sure this option available. The ability to find a matching bone marrow donor prevents many patients in need from receiving a transplant. However, a novel BMT trial using half-matched donors, is allowing many more patients to receive a bone marrow transplant. It is currently available to patients with refractory and/or relapsed high risk leukemias and lymphomas. This trial is only available at Hopkins and is helping patients in the U.S. and around the world. Results have been favorable, with safety and toxicity comparable to matched transplants. As a result, the strategy is now being used earlier in the treatment of leukemias and lymphomas, and could soon be used expanded to include children with solid tumors such as sarcoma and neuroblastoma.
In the laboratory, Dr. Symons is developing a strategy to awaken the patient’s immune system and cause it to attack tumor cells. The immune system becomes tolerant of tumor cells, but by giving donor immune cells called lymphocytes, she is able to achieve a temporary attack against the cancer. To extend the response, Dr. Symons is utilizing other tools, such as radiation therapy and cryotherapy (freezing tumor cells), to cause the immune system to recognize cancers cells as foreign and dangerous
Dr. Christopher Gamper also is studying the regulation of the immune system and has focused on a cancer-linked biochemical activity known as DNA methylation for its ability to deactivate circulating immune system T cells. Using drugs to block T cell DNA methylation could prevent cancer cells from evading T cells. In a mouse model of an aggressive cancer, Dr. Gamper showed that demethylated T cells were more effective against tumor cells. This targeted approach could help clinicians obtain improved responses against difficult pediatric cancers without toxicities of extensive chemotherapy and radiation treatment.
Pediatric Brain Tumors:
Brain tumors are the second most common group of cancers seen in children and the most common group of solid tumors. Each year, more children die of brain tumors than any other form of pediatric cancer. The Pediatric Neuro-Oncology Program at the Johns Hopkins Kimmel Cancer Center, directed by Dr. Ken Cohen, is one of the largest of its kind in the country. Each year over 80 children are diagnosed and treated at Johns Hopkins and an additional 80 to100 second opinions are provided through our multidisciplinary program.
Therapy for these patients is very complicated because some of the mainstays of treatment for tumors in other parts of the body cannot be used as aggressively because they are too harmful to children’s brains. Surgery offers limited benefits, and treatment with radiation therapy can result in severe and long term cognitive and developmental problems for children. As a result, new treatment approaches are often used.
Arsenic appears to target certain molecular pathways important to the development of certain common pediatric brain tumors. As a result, Dr. Cohen, who also is Clinical Director of Pediatric Oncology, is leading the first trial in children to combine the drug arsenic trioxide and radiation together in the treatment of children with the most aggressive forms of brain tumors. Another trial involves the first study of a new drug that targets the common cancer-gene pathway Hedgehog in certain patients with brain and other solid tumors.
Brain stem gliomas are perhaps the most challenging of all the pediatric cancers. Despite our best efforts, there are currently no children cured of this type of cancer. In a new targeted treatment approach, the cancer drugs cetuximab and irinotecan are be given to children with brain stem gliomas and another treatment-resistant form of brain cancer known as high-grade astrocytoma. The drugs work by blocking a gene pathway known to be involved in the growth of these tumors.