By Janet Ball
in San Francisco
A nine-year-old boy with leukaemia has inspired a video game to help children understand and deal with cancer.
Ben wanted a game that could explain how cancer worked
In many ways, Ben Duskin is a typical American nine-year-old, playing video games whenever time, or his mother, will allow.
But Ben is also unusual, because he is able to say he has designed one of his very own.
When Ben was five, he was diagnosed with leukaemia, and his mother tried to explain his treatment by likening it to the classic Pac Man video game, gobbling up the bad cancer cells.
But the problem was that Ben had never played Pac Man, and so he decided a new game was needed for children with cancer, to help them understand and deal with their illness.
He put this request to the Make a Wish charity in San Francisco, causing them a great deal of heartache, according to the head of the office, Patricia Wilson.
"Some people almost laughed when I presented the request," she told the BBC programme Go Digital, "just saying do you understand what you're asking for? This is not possible, this is millions of dollars. This will take several years in the development."
Just when it seemed Ben's wish was too much to ask for, someone stepped forward and offered to make it happen.
Eric Johnston worked closely with Ben to design the game
That person was Eric Johnston, a programmer with LucasArts video games. He worked with Ben every week over the months to create the game just how the boy wanted it.
"Ben knew about the different side effects he wanted to portray in the game," said Mr Johnston.
"He knew there would be attributes that the player would have - health from the hospital, ammo from the pharmacy and attitude, which you get from home.
"And as you go through the game you hit some setbacks - electrified barriers - which makes you lose some attitude, which according to Ben is pretty much how it works."
The free game, which shows Ben whizzing around the screen on his skateboard, has already been downloaded more than 35,000 times.
Eric and Ben have received messages from hundreds of people including doctors and game designers.
According to Ben, the most important people are the children who are in the position he was once in.
For that reason he and Eric wanted to keep the game quite simple, so that even young children can play and understand it.
The player faces monsters representing the side effects of cancer. A fever monster throws fireballs, a giant, evil chicken represents chicken pox and a robot called Robarf hurls a green gooey mess - the sickness most children with cancer will face.
While they can be battered by the monsters and have to use up some of their health to destroy the cancer cells, the player cannot be killed off in the game.
Ben insisted on this, in order to send a clear message to other children.
"I just want them to learn what the medicine is doing to their body and how it's helping it," he explained.
"And I hope that they'll learn not to give up, to stick with it or you won't make any progress. And to just hang in there and have fun."
To play Ben's Game, go to www.makewish.org/ben where you can download the game, as well as read messages from Ben and find out more about the project.
You can hear more about Ben's Game on the BBC World Service programme, Go Digital