High-grade PIN : Flat type
In the initial stages of proliferative changes of high-grade PIN, epithelial hyperplasia is minimal. The atypical cells form two to three layers of cells arranged in an orderly fashion around the gland. This is the flat subtype of high-grade PIN. The image shows one such gland sectioned longitudinally. Note the nuclear enlargement and hyperchromasia, prominent nucleoli, and apical snouts of the acinar cells.