Light micrograph section through human brain tissue showing a neuro astrocytoma. An astrocytoma is a tumour that arises from the star-shaped cells (astrocytes) that form the supportive tissue of the brain. Other supportive cells of the brain include oligodendrocytes and ependymal cells. Collectively, these cells are known as glial cells and the tissue they form is known as glial tissue. The cause of most astrocytomas is not known. However, exposure to ultraviolet rays, certain chemicals, ionising radiation and stress could be a contributing factor in the cause of this type of cancer.