A general cell goes through the mutations to turn into a cancerous substance as it differentiates, and there are replication errors related to each cycle. Additionally, the environmental elements may also donate to the mutations that acclimatize in the mitotically active cells.
However, the neural cells are quiescent and do not undergo the process of mitosis, and thus, cannot encounter with a cell cycle associated mutational incident that results in cancer. Hence, it is unusual.