[3] Primary gliosarcoma (PGS) is classified as a grade IV tumor and a subtype of glioblastoma multiforme in the 2007 World Health Organization classification system (GBM).

[4] Because of a lack of specific and clear diagnostic criteria, the word "gliosarcoma" was frequently used to refer to glial tumours with mesenchymal properties,[5] such as the ability to make collagen and reticulin.

Although most gliomas rarely show metastases outside the cerebrum, gliosarcomas have a propensity to do so, most commonly spreading through the blood to the lungs, and also liver and lymph nodes.

[10] Early reports claimed that the hyperplastic blood vessels that are frequently present in high grade gliomas underwent neoplastic change to become the sarcomatous components.

[6] Feigin's early reports components of perivascular sarcomatous and hyperplastic arteries in gliosarcoma offered evidence for the "collision tumor" hypothesis.