A Canadian-led international research team has identified a new and potentially less life-threatening form of retinoblastoma, an eye tumour that occurs in very young children and can lead to the loss of at least one eye.
Retinoblastoma is rare, affecting about one in 20,000 children. In Canada, about 25 children under age five are diagnosed each year with the tumour of the retina, the light-sensitive tissue at the back of the eye that detects light and colour.
For years, it was thought that the rapidly growing cancer was always caused by a mutation in a single gene, called the RB1 gene.
Now researchers at Toronto's Hospital for Sick Children and international collaborators have determined there is another type of the disease caused by a different gene, a cancer gene, which will change how doctors treat patients with this form of tumour.
"Everyone in the world thought retinoblastoma was one cancer that was initiated by the retinoblastoma gene, only one kind of cancer, although there are two forms," said principal researcher Dr. Brenda Gallie, a world-renowned expert in the disease.
Both these forms result from the deletion of RB1, a tumour suppressor gene whose job it is to regulate cell growth and keep cells from dividing too rapidly or in an uncontrolled way.
In about 60 per cent of cases, the RB1 gene is missing from cells in the retina, and patients are not at risk of passing the disease to their offspring.
But for the remaining children, the genetic mutation is present in all the cells of their body. Usually, the mutation arises spontaneously around the time of conception, but in 10 per cent of cases, the mutated gene is inherited from a parent.
These youngsters often develop tumours in both eyes. And although retinoblastoma has a high cure rate in developed countries like Canada, survivors have an elevated risk of developing another form of cancer later in life, Gallie said.