Thirty years ago, a number of the basics were understood about childhood leukemia. The various forms of the disease were recognized and some of the key treatments to treat it were already in use. But, up until the early 1970s, overall cure rates and survival among children with leukemia were ‘abysmal’, according to Dr. David Mitchell, assistant professor of paediatrics at McGill University.
During the 1970s, survival rates improved dramatically after findings from two large international clinical trials from the Pediatric Oncology Group (POG) and Children’s Cancer Group (CCG) showed that giving kids more aggressive chemotherapy (anticancer drugs) led to better outcome.
“People started to use chemotherapy more widely in the late 60s, and began to get some cures. Cure rates jumped up to around 10% to 20% in the late 60s and early 70s,” he said. While increased numbers of children were cured of the disease, most relapsed. In those patients, cancer cells began to show up in their spinal fluid – a place where chemotherapy couldn’t reach.
Another approach to get at cancer cells in spinal fluid was radiation therapy. Here, all patients were given radiation to the brain and spinal cord to boost therapy to the central nervous system (CNS) in order to prevent relapse. But this led to problems, affecting intelligence and behaviour, and so was mostly abandoned.
Eventually, researchers found ways to administer medications directly into the spinal fluid, which helped to prevent CNS relapse.
Leukemia is a rare disease but is the most common of all childhood cancers. It accounts for 30% of all cancers diagnosed in children aged 15 or less. Acute lymphoblastic leukemia (ALL) is the most common form and accounts for close to 75% of cases. Another important type is acute mylocytic leukemia (AML) making up about 15% of cases.
The cure rate for childhood ALL is 80% to 85%, but only about 50% to 55% for tougher-to-treat AML. Generally, there hasn’t been a big change in the medications given to leukemia patients, Dr. Mitchell said. “The real advances to date are in the accumulated knowledge and technologies that help to define how aggressive a leukemia is,” he said.
“Now, we can stratify the therapy. If somebody has low-risk disease, you don’t hit them over the head with biggun chemotherapy. You treat them with the least toxic chemotherapy that’s going to give a good cure rate,” he said. Unfortunately, there remains a minority of children with a complex form of the disease that doesn’t respond well to any treatments.
Work is being done on new types of drugs that can zero-in on and target cancer cells. Several drugs are now being studied for both ALL and AML, but it’s hard to say which ones will prove to be truly effective.
Genetic research may lead to new types of treatments.