Tubular Pyloric Gland Adenoma of the Left and Right Hepatic Ducts: Report of a Unique Case With Immunohistochemical and Molecular Studies.

Pyloric gland adenomas (PGAs) of the extrahepatic biliary system are rare lesions. We report a case of a tubular PGA that led to biliary obstruction. The tumor was located at the confluence of the right and left hepatic ducts, extending to the left hepatic duct. The tumor cells expressed MUC6 and MUC5AC. MUC1 and CD10 were focally positive. MUC2, p53, and CDX2 were not expressed. The Ki67 positivity was estimated at <15%. None of the KRAS, NRAS, BRAF, EGFR coding regions resulted in clinically relevant amino acid substitutions. SNP rs1050171 (EGFR p.Q787Q, silent mutation) corresponding to c.2361G>A transition in exon 20 was noticed. Awareness of this rare lesion is important for pathologists and clinicians alike, because it may cause significant morphologic and clinical difficulties, especially when presenting as an obstructive mass. Because of the possible risk of evolving malignancy, surgical resection is recommended whenever possible.