Table 1.

Classification and characterization of biliary intraepithelial neoplasia (based on Ainechi S, Arch Pathol Lab Med 2016).

	BilIN-1	BilIN-2	BilIN-3
Cells	Polarity maintained Increase in basally placed nuclei	Loss of polarity Nuclei reaching the luminal surface	Marked loss of polarity Nuclei reaching the luminal surface
Nuclei	Mild atypia	Moderate atypia	Severe atypia
Architecture	Flat	Flat or micropapillary	Likely micropapillary
Mitosis	Rare	Rare	Likely
Dysplasia	Low-grade	Intermediate	High-grade/carcinoma in situ