Knowledge Shot: Glioblastoma

In glioblastoma, ”-blastoma” refers to a malignant, or invasive tumor, formed by immature, precursor cells, often called blasts, and “glio-“ to glial cells, particularly astrocytes, which make up the “glue” or supportive tissue of the central nervous system, so glioblastoma is basically an aggressive cancer of the central nervous system that arises from precursor glial cells specifically bound to differentiate into astrocytes.

Actually, this is the most common primary malignant tumor of the central nervous system in adults, with “primary” meaning that it originates inside the central nervous system.

Okay, normally, the human central nervous system, aka the brain and spinal cord, apart from neurons, contains trillions of another type of cells, known as glia.

Glial cells are sort of the “glue” of the nervous tissue, but they are also involved in every single aspect of neuronal function.

There is a wide variety of glial cells, but all of them originate from some common precursor cell that, through various steps, chooses to differentiate into a specific type of glial cell.

The most abundant one is the astrocyte. In greek, “astro” means star, so astrocytes are star-shaped cells, each of which has thousands of projections waving around and taking up neurotransmitters, cleaning up after neuronal activity, while also surrounding the endothelial cells that line the brain capillaries, in order to help create the blood- brain barrier.

What sets them apart histologically is that they express high amounts of an intermediate filament protein, called glial fibrillary acidic protein, or GFAP for short.

Now, sometimes, astrocytes or their precursors develop mutations in genes controlling their replication.

More specifically, there are typically mutations that lead to overexpression of genes promoting cell proliferation, such as growth factor receptors, and others that cause loss of function of tumor suppressor genes, such as p53.

The net result is that cells start multiplying out of control forming tumors known as astrocytomas.

As if this were not enough, cancer cells tend to lose morphological and functional features of normal cells of the astrocytic lineage.

So, depending on how normal or abnormal these cells look, tumors are “graded” on a scale from I to IV.

Most astrocytomas in adults are high grade and grade IV are specifically called glioblastomas.

Sometimes, even lower- grade astrocytomas can get more aggressive through additional gene mutations and progress to what is known as secondary glioblastomas.

In any case, cells of glioblastomas replicate at an extremely rapid pace, which allows the tumor to quickly reach an enormous size and invade the adjacent nervous tissue.

Most of these tumors are located in one of the cerebral hemispheres of the brain but they grow so large that it’s classic for them to even cross the corpus callosum, which is the midline structure joining the two cerebral hemispheres and produce the image of a butterfly, which is why some call them butterfly gliomas.

Even though cancer cells manage to recruit abundant blood vessels to get them nourished, they proliferate so fast that even this increased oxygen and nutrient supply is not enough.

This forces a lot of them, especially in the center of the tumor, where the blood vessel network is not so dense, to die and accumulate forming areas of necrosis.