Table 1.

Classification of human and mouse PanIN progression

Normal duct	Flat, cuboidal or low-columnar epithelium, without mucin accumulation, nuclear crowing or atypia
PanIN-1A	Tall columnar cells organized in flat epithelium, with basal nuclear localization and mucin-rich cytoplasm.
PanIN-1B	Identical cellular morphology to PanIN-1A, but organized in papillary, micropapillary or basally pseudostratified arrangements.
PanIN-2	Flat or (more commonly) papillary architecture, with nuclear abnormalities that may include loss of polarity, crowding, enlargement, pseudostratification and hyperchromatism.
PanIN-3	Papillary or (less commonly) flat architecture, with loss of nuclear polarity, dystrophic goblet cells, occasionally abnormal mitoses and prominent nuclear abnormalities. Cribiform achitecture or luminal “shedding” of viable or necrotic cells frequently observed.

Key morphological characteristics of preinvasive pancreatic ductal lesions in the human and mouse, as defined by pathologist working groups of the Pancreatic Cancer Think Tank and Pancreatic Cancer in Mice and Man conferences, respectively (Hruban et al. 2006; Hruban et al. 2001). Progression to pancreatic ductal adenocarcinoma (PDAC) is defined by invasion of tumor epithelial cells through the basement membrane. Additional diagnostic information is available in the original publications, and online at the Sol Goldman Pancreatic Cancer Research Center of Johns Hopkins Medicine: http://pathology.jhu.edu/pc/professionals/DuctLesions.php