Answer and Discussion of Quiz Set: N-024

2.    Which of the following morphologic features is sufficient to make a diagnosis of glioblastoma when the other features are compatible with such diagnosis?  Answer

A.  Increased mitosis

B.  Endothelial proliferation.

C.  Patchy distribution of positive immunoreactivity for glial fibrillary acidic protein (GFAP)

D.  Increased nulcear pleomorphism

E.  Presence of sarcomatous component that is non-immunoreactive to GFAP

Answer and Discussion: The answer is B. As per the WHO classification, "Prominent microvascular proliferation and/or necrosis are essential diagnostic features". Increased mitosis and nuclear pleomorphism are common features of high-grade astrocytomas. It is necessary for a diagnosis of anaplastic astrocytoma but is not sufficient for a diagnosis of glioblastoma. High-grade gliomas often, but not always, have uneven distribution of immunoreactivity for GFAP. The presence of sarcomatous component that is non-immunoreactive for GFAP should lead to a consideration of gliosarcoma. By itself, it is not a required diagnostic feature of glioblastoma.