Intestinal lamina propria-type tumor stroma characterizes type 2 but not type 1 intraductal papillary neoplasm of the bile duct

The pathological differentiation of type 2 intraductal papillary neoplasm of the bile duct (IPNB) from type 1 is important. Utilizing 19 type 1 and 20 type 2 IPNB surgical specimens, the presence of pericryptal myofibroblast-like cells (PCMLCs) and amounts of IgA- and IgG-positive plasma cells (IgA-P, IgG-P), and CD117-positive mast cells (mast cells) and their diagnostic utility for IPNB typing were analyzed. PCMLCs were defined as SMA-positive and CD31/ CD34/von Willebrand factor-negative spindle cells. Next, five type 1 and six type 2 biopsy samples were evaluated for diagnostic applicability. As results, PCMLCs were absent in all type 1 cases except for the oncocyic subtype and present in all type 2 cases. IgA-P, IgG-P, and mast cells were significantly more abundant in type 2 than type 1. Receiver-operating characteristic analysis identified diagnostic cutoff values. All type 2 biopsy specimens, but none of the type 1, harbored PCMLCs. The established cutoff values were valid in most (> 80%) cases across both groups. In conclusion, type 2 IPNB is characterized by iLP-type stroma featuring PCMLC formation and abundant IgA-P, IgG-P, and mast cell-infiltration, whereas type 1 IPNB is not. Combined IgA quantification and PCMLC detection may provide a robust diagnostic approach for IPNB typing.