Like most children of her age, Kara Siert has a vivid imagination and loves writing about fantastical worlds and adventures with dragons and talking animals.

Like most children of her age, Kara Siert has a vivid imagination and loves writing about fantastical worlds and adventures with dragons and talking animals.

But three years ago, the young Suffolk writer was given the devastating news that she could lose her writing hand after being diagnosed with bone cancer.

Now the 12-year-old is not only on track to making a full recovery after 10 months of chemotherapy and five operations on her right arm, she is also proving to be an inspiration to millions by publishing a book of short stories and speaking about her treatment to local schoolchildren.

Kara, who lives at RAF Lakenheath with her US Air Force parents, is set to realise another dream next week after being invited to a party at 10 Downing Street to mark the birthday of a national children's charity.

The youngster spoke of her excitement yesterday as she prepares to meet the prime minister's wife, Sarah Brown, on Monday with 19 other terminally and seriously ill children and their families to celebrate the 20th anniversary of the Dreams Come True charity.

Kara, who moved from Nebraska, USA, to Suffolk with her family in 2005, had only been in the country for a couple of months when she started complaining about pains in her right arm. Then, just before her 10th birthday, an x-ray revealed that she had a large tumour in her upper arm, which was later diagnosed as osteosarcoma - cancer of the bone.

But despite going through chemotherapy and having the cancerous bone in her arm replaced with a titanium rod, the brave girl continued to write short fantasy stories about the mystical fictional world of Cunburra.

Dreams Come True, which has helped more than 3,500 terminally and seriously ill children over 20 years and assisted Kara to publish a book of 18 short stories entitled Tales of Cunburra and Other Stories in 2006, has now invited the young author and her mum to Downing Street on Monday.

The schoolgirl, who has now sold 500 copies of her first book, has been in remission for almost two years and has now started writing about her cancer. For the last year she has also been visiting schools at Lakenheath to talk about her life, treatment and her stories.

Linda Siert, whose husband Ward is a flight commander for the emergency services hospital and 48th Medical Group at RAF Lakenheath, said her daughter was a “marvel”.

“We are continually amazed by what she continues to come up with. She has not stopped writing ever since she picked up a pen.

“Her dream is to continue to write and as an individual to become a published author.

“When the children ask her about her cancer she almost completely ignores how difficult it was. The whole experience of finding out your child has cancer and watching her suffer was the worst nightmare of our lives.

“We feel she has the best possible chance of the cancer not coming back. She just remembers the good things like the friends she has made, the book that was published and the fact that she is still alive and still has her arm,” said Mrs Siert.

Kara, who was born in China and was adopted when she was 11 months old, says her favourite book is the Chronicles of Narnia by CS Lewis. She added that it would be “really cool” if she could get more work published.

“It is really exciting. I never imagined that I would get to go to Downing Street and have tea with the prime minister's wife,” she said.