The standard for materiality is generally interpreted to be 5% of certain line items. In other words, a misstatement of an item that is less than 5% will be considered immaterial while those 5% or more will be material. Obviously a company like ExxonMobil with several hundred billion in revenue and assets has a different materiality threshold than your local barbershop.
Given the shrinking size of NWBO's financial statements, it wouldn't take much of a misstatement to rise to the level of materiality, especially with respect to revenue.