A. A measurable increase of the plexiform neurofibroma (greater than or equal to 20% increase in the volume, or a greater than or equal to 13% increase in the product of the two longest perpendicular diameters, or a greater than or equal to 6% increase in the longest diameter) over the last two consecutive scans (magnetic resonance imaging (MRI) or computed tomography (CT), or over the time period of approximately one year prior to evaluation for this study.