Ashya King, 5, had proton beam therapy and appears to have had no cancer for months, Jonathan Hartley said.
The family is in Spain. Ashya's parents, Brett and Naghmeh King, are afraid to return to the United Kingdom for fear of arrest, though they are in talks to return, Hartley said.
That announcement came after they were arrested in Spain while authorities decided whether to charge them and extradite them to Britain. The Kings had serious concerns about the medical treatment that Ashya was receiving at University Hospital Southampton. So they defied doctors' orders and took him out.
Dr. Hernan Cortes Funes, who's overseeing Ashya's treatment, agrees with the assessment that Ashya is cancer-free, he told CNN on Monday. Still, there is a high chance of recurrence, he said.
Funes gave CNN details:
In August, Ashya had surgery in Britain to remove the tumor. The kind of tumor Ashya had is very aggressive and can often relapse in the brain or the spinal cord. The standard treatment is radiotherapy in the brain and spinal cord, which can cause serious side effects or even death.
Ashya's parents wanted to instead do a new proton therapy, which is conducted by only a few sites in Europe. One is in the Czech Republic. Since Ashya was born in Marbella, southern Spain, his family contacted a hospital there and then took Ashya to have proton therapy in Prague in September. The next month, the boy began rehabilitation in Marbella.
Initially after the proton therapy, Ashya was mute and had no movement. But after three months of intensive treatment, he can walk generally unaided. He has also been swimming and playing with toys, Funes said.
His family comes to see him every day. Ashya has difficulty speaking but continues to improve. He can say a few words, and he can give simple answers when asked questions such as whether he is hungry.
Medical officials in Madrid will make a molecular profile of the tumor that was removed to help identify the risk of relapse. Doctors have requested a sample from Southampton.
The surgery conducted in Southampton was excellent, Funes said.