As the family of Leeds' toddler Pippa Gibb open up about her battle with a rare cancer, we explore what it is.
Langerhans' cell histiocytosis (LCH) is a very rare condition with a high survival rate, which has recently been recognised as a kind of cancer.
According to Great Ormond Street Children's Hospital (GOSH) it comes from when the body produces too much of a certain kind of cell, which moves around the body, causing damage.
It can affect bones or organs, and the symptoms can vary from breathing difficultiies, a skin rash to lumps on the skull or a swollen tummy.
It is a very rare condition, with just 50 children diagnosed every year in the UK. It is more common in boys than girls.
The cause is unknown.
The illness is treated with chemotherapy, and survival rates are very high, with 90 per cent of children cured from LCH.
Even if the cancer returns, treatment is effective if it has to be started again.
Children can be left with ongoing health problems as a result of the cancer, but this is dependent on where it is.
Those with pituitary disease require ongoing life long hormone therapy.