Four times as many youths now survive cancer compared to decades ago, a US study has found.

Modern medicine has made huge strides when it comes to treating children with cancer, and four times as many youths now survive cancer compared to decades ago.

Life expectancy after a battle with peadiatric cancer is also longer than it used to be, according to the findings released at the American Society of Clinical Oncology annual meeting.

The study was based on an analysis of more than 34,000 participants in the federally funded Childhood Cancer Survivor Study, which follows five-year survivors of childhood cancer diagnosed between 1970 and 1999 at 31 US and Canadian hospitals.

"Fifty years ago, only one in five children would survive cancer, and today over 80 per cent are alive five years after diagnosis," said lead study author Gregory Armstrong, a pediatric oncologist at St Jude Children's Research Hospital.

Child cancer survivors still face an increased risk of heart disease and a second cancer in the future, but improvements have been made by offering more refined and less harsh treatments than in the past, he added.

"Now, we've not only helped more children survive their primary cancer, but we've also extended their overall lifespan by reducing the overall toxicity of treatment in more modern eras."

Researchers found that among children who live five years after a diagnosis - those known as five-year survivors - only six per cent are expected to die in 15 years' time.

That's a big improvement over the 1970s, when there was a 12.4 per cent mortality rate among children with cancer after 15 years.