Anaplastic (from Greek *ana-* = backward + *plasis* = formation) refers to cells or tissues that have lost their normal structure and differentiation, indicating malignant transformation.

Anaplastic cells typically show:

• High mitotic activity
• Nuclear atypia (abnormal nuclear shape and size)
• Increased cellularity
• Loss of normal tissue architecture
• Often poorly differentiated or undifferentiated

In the context of brain tumors:

• Anaplastic gliomas are classified as WHO Grade 3
• They are malignant and infiltrative, but do not show necrosis or microvascular proliferation (hallmarks of Grade 4)
• Common anaplastic gliomas:
  • Anaplastic astrocytoma
  • Anaplastic oligodendroglioma

“Anaplastic” denotes malignancy with loss of differentiation, often used in the classification of Grade 3 tumors to indicate a more aggressive behavior than low-grade (Grade 1–2) tumors.