Glioblastoma brain tumour. Light micrograph of a section through a glioblastoma brain tumour. This is a cancer of glial tissue, the supportive tissue in the brain. Normal brain tissue has a regular appearance, but the cells seen here vary greatly in size and shape. Glioblastomas are aggressive cancers, growing rapidly and invading surrounding tissue. The symptoms depend on the region of the brain affected, but can include seizures, headaches and speech disturbances. Glioblastomas are difficult to treat and the prognosis is poor.