A child who had neuroblastoma, a type of nerve cell cancer, has survived over 18 years after an experimental treatment, medical researchers said on Monday, highlighting the therapy’s long-term efficacy in boosting the immune system to fight cancer.

The US researchers at the Baylor College of Medicine, Texas Children’s Hospital have said the follow-up observations mark the longest reported survival after chimeric antigen receptor (CAR)-T cell therapy for active malignancy without the need for any additional treatments.

CAR-T therapy is a treatment designed to genetically modify a patient’s immune T cells — a type of white blood cells — to recognise and attack cancer cells more effectively. CAR-T therapy is approved for several blood cancers, including leukaemias and lymphomas, and researchers have been exploring its use in solid tumours.

Helen Heslop, a professor of medicine and paediatrics at Baylor College, and her colleagues had conducted a safety and preliminary efficacy trial of CAR-T therapy on 19 children with neuroblastoma between 2004 and 2009.

Neuroblastoma is a rare type of solid tumour that doctors view as challenging to treat because of its high relapse rates despite conventional therapy. The five-year survival rates in neuroblastoma range from 95 per cent in low-risk patients to 90 to 95 per cent in intermediate-risk patients to 50 per cent in high-risk patients.

The CAR-T cells the Baylor College team used were engineered to recognise a protein called GD2 abundant in neuroblastoma cells.

While the trial established that CAR-T is safe, among the 19 patients, 12 died between two months and seven years after treatment after a neuroblastoma relapse.

Among the seven other patients, one was followed up for eight years, a second was followed up for 10 years, and five patients continued to be followed up for more than 13 years to more than 18 years.

The patient who is alive at over 18 years had bone lesions at the time of treatment, has never required any other therapy and is likely the longest-surviving patient with cancer who had received CAR-T therapy, the researchers said.

“Encouragingly, she has subsequently had two full-term pregnancies with normal infants,” Heslop and her colleagues said, reporting their findings in the journal Nature Medicine.

The data show that the short-term and medium-term benefits of CAR-T therapy in patients with neuroblastoma are also sustained in the long term, they said.