Different paediatric brain tumours originate from the same type of cell

Malignant brain tumours in children are typically treated through a combination of surgery, radiation therapy, and chemotherapy, which today result in cure in roughly three out of four cases. In recent years, researchers have identified nearly a hundred different types of cancer in the brain, but the relationships between them have remained insufficiently mapped. For example, it has been unclear which tumour types are most closely related and might therefore be treated in similar ways.

Striking similarities to other tumours

In the new study, Fredrik Swartling and his research team at IGP, in collaboration with international colleagues, investigated the development of pineoblastoma, a serious tumour originating from the pineal gland, a small pinecone-shaped structure located deep in the middle of the brain.

When the researchers analysed tumours from patients using advanced molecular methods and compared them to other tumour types, the results were unexpected – the tumours did not resemble other tumours from the same brain region. Instead, they showed striking similarities to tumours arising in entirely different parts of the brain, especially to the eye tumour retinoblastoma that arises in the retina at the back of the eye and to medulloblastoma that forms from cells in the cerebellum, situated at the rear of the head.

“We observed, for example, that a tumour discovered in the pineal gland of a patient was so similar to a tumour typically found in the cerebellum that we initially suspected it might have spread from there. But this turned out not to be the case. The cells that gave rise to the tumours were biologically very similar to one another, despite originating in such different areas of the brain,” says Fredrik Swartling, senior author of the study.

Tumours could be treated in similar ways

In the pineoblastoma cases examined, the researchers found that the tumours originated from a particular type of immature precursor cell that also produced a protein commonly found in light-sensitive cells, namely, the cells of the retina.

“Cells that detect light for vision exist only in the eye in humans. But over the course of evolution and in other animal species, cells that respond to light or that retain proteins called photoreceptors are also found in other parts of the brain,” says researcher Miao Zhao, who performed the experimental cell and animal model studies in the laboratory.

It is precisely these cell types, cells that still carry features associated with photoreceptors, that appear capable of not only giving rise to retinoblastoma in the eye but also giving rise to pineoblastoma and medulloblastoma in the developing brain in children. The researchers confirmed this connection in mouse models, where activation of the photoreceptor-driven cells triggered the development of pineoblastoma. If the photoreceptor activity was further blocked using the genetic scissors CRISPR/Cas9, these tumours stopped growing.

“The fact that cells with photoreceptor activity are particularly prone to developing tumours suggests that we may be able to target them with future precision therapies. Our findings also indicate that tumours that arise in the pineal gland and in the cerebellum can in fact be treated in similar ways,” says Fredrik Swartling.

The study was performed in collaboration with Paul Northcott at St. Jude Children’s Research Hospital in Memphis, USA, and Mariella Filbin at Boston Children’s Hospital, USA, as well as collaborators from Canada, Germany, and Austria. It received financial support from the Swedish Childhood Cancer Fund, the Swedish Cancer Society, the Swedish Research Council, the Swedish Brain Foundation, and the NIH, and is published in the scientific journal Cancer Cell.