The drug is showing impressive success in treating children with polymetastatic Ewing sarcoma

Ewing sarcoma is one of the most common bone cancers seen in children, and if it spreads, it can be fatal. One study found that less than a quarter of children with polymetastatic Ewing sarcoma survived five years after their diagnosis. Now scientists have found that a drug called pazopanib has had impressive success in treating a small group of young patients. 85% of their patients survived two years after diagnosis, and two-thirds did not see disease progression. The team is calling for larger studies that can further develop this treatment.

“Survival rates were higher than in historical controls, suggesting that it can extend lives and, importantly, do so without adding serious toxicity,” said Professor Anna Raciborska of the Warsaw Mother and Child Institute, lead author of the paper in Frontiers in Oncology. “In addition, the quality of life of the treated children was good. After the end of intravenous therapy, patients could receive pazopanib as a treatment at home.”

While we await new treatment options, it is possible to apply this existing drug to improve outcomes in very high-risk patients. It opens the door to targeted therapies earlier in the course of the disease, potentially improving survival and quality of life.”

Prof. Anna Raciborska, Warsaw Mother and Child Institute

A potential lifesaver

Pazopanib was originally developed for renal cell carcinoma. But after some success in adult Ewing sarcoma patients, Raciborska and her team tried to incorporate it into the regimens of children with polymetastatic Ewing sarcoma, hoping that combining it with other treatments would give better results by targeting different aspects of the cancer at the same time.

“Pazopanib is a pill that blocks the tumor’s ability to grow new blood vessels, which tumors need to survive and spread,” Raciborska said. “By cutting off this ‘blood supply’, the drug apparently makes tumors weaker and more sensitive to chemotherapy and radiation. This can slow down the disease and help existing treatments work better.”

Between 2016 and 2024, 11 young patients were given pazopanib alongside standard first-line treatments at the Warsaw Mother and Child Institute. The success of this additional treatment was monitored as part of their routine care, with imaging and laboratory tests and careful monitoring of any potential side effects. The goal was to determine whether the additional treatment helped control their cancer and whether any side effects were manageable.

A ray of hope

The 11 patients were between five and 17 years old when they started taking pazopanib. They received pazopanib during and after their chemotherapy, although treatment was stopped for surgery and stopped if the disease progressed or patients experienced unacceptable side effects. On average, patients received pazopanib for 1.7 years. At the time of writing, six were still receiving pazopanib.

Five children underwent surgery for their primary tumor, while three received stem cell transplants and 10 radiation therapy. Imaging showed that all but one patient was clearly responding to treatment. One child’s cancer progressed, two relapsed and one sadly died – but 10 patients are still alive. Although combining cancer therapies carries a risk of increased treatment toxicity, pazopanib was also very well tolerated, with minimal, treatable side effects.

The scientists calculated a two-year overall survival rate of 85.7%, while 68.2% of patients reached the end of the second year without a new “event,” meaning their cancer remained stable. This is a better result than a previous study in adult patients, suggesting that pazopanib could be more effective and better tolerated in children or when given earlier in treatment.

However, the researchers stress that much more work needs to be done in larger groups of patients to validate these exciting early results. Polymetastatic Ewing sarcoma is rare, so there are few large-scale randomized clinical trials targeting it. But while new treatments are being developed, researchers are encouraging the scientific community to test the use of pazopanib as an option to further help children with severe metastases.

“While the results are encouraging, larger controlled trials are needed before standard practice changes,” said Raciborska. “Our study could serve as a basis for setting up prospective, multicenter clinical trials to confirm these promising results. However, this requires a lot of work and commitment of resources. Perhaps future EU programs will allow this. We hope this will be possible.”