 Thus the main difference between Gleason 1 and 2 is the density of packing of the glands seen and invasion is possible in Gleason 2,  not in Gleason 1 by definition.
<clarity>  Thus the main difference between Gleason 1 and 2 is the density of packing of the glands seen and invasion is possible in Gleason 2,  not in Gleason 1 by definition.
 Thus the main difference between Gleason 1 and 2 is the density of packing of the glands seen and invasion is possible in Gleason 2, not in Gleason 1.