Criteria for malignancy: invasion of cells through the basement membrane
Histologic patterns of PanIN:
(1) flat
(2) basal pseudostratified
(3) micropapillary
(4) papillary
Features of PanIN-3:
(1) true cribriform pattern
(2) luminal necrosis
(3) budding off of small groups of cells into the lumen
(4) dystrophic goblet cells
(5) frequent mitoses
(6) abnormal and/or apical mitoses
(7) large, crowded nuclei with loss of polarity
(8) macronuceloli
Features of PanIN-1:
(1) none of the features for PanIN-3
(2) no or very rare mitoses
(3) small, round or oval nuclei with preserved nuclear polarity (perpendicular to the basement membrane) and little crowding
(4) abundant supranuclear mucin
If PanIN-1 shows a flat pattern, then it is termed PanIN-1A. Else (any other pattern) PanIN-1B.
Features of PanIN-2: features in between PanIN-1 and PanIN-3:
(1) rare to few mitoses, with nonapical (nonluminal) mitoses
(2) slight increase in nuclear size with or without crowding
(3) may show some loss in nuclear polarity
