A previously fit and healthy amateur boxer is taking on his biggest fight yet - a form of children's cancer rarely seen in adults.Christopher Sparks, 37, was diagnosed with neuroblastoma last year after feeling ill following a holiday to Turkey.But doctors believe his tumour may have first started growing ten years ago - despite his active lifestyle.Christopher has since undergone several rounds of chemotherapy and radiotherapy to eradicate the disease, and is on track to beat it with further intensive treatment.Neuroblastoma is rarely seen in children, let alone adults - affecting around 100 youngsters in the UK each year.Christopher said medics told him he is just one of two adults in the nation diagnosed with the condition at the moment.