April 2021 — Gastroenterology and Surgical Pathology Case 1

The diagnosis in this case is: MUC1 (+), MUC2 (-).

The gross photograph shows a well-circumscribed mass contained within a dilated bile duct. Microscopy shows papillary projections of biliary epithelium seated within a bile duct with focal invasion. This leads to a diagnosis of invasive carcinoma arising within an intraductal papillary neoplasm of the bile duct (IPNB). 

IPNB is essentially the biliary counterpart to intraductal papillary mucinous neoplasm (IPMN) of the pancreas. Similar to IPMN, IPNB has four morphologic subtypes. The distinction of these subtypes can be aided by their staining patterns for antibodies against two mucin core (MUC) proteins, MUC1 and MUC2.

The pancreaticobiliary subtype displays tall, columnar cells that approximate normal biliary epithelial cells. This is the most common subtype of IPNB, as well as the one most associated with invasive components, and is also the one seen in this case. It is typically positive for MUC1 and negative for MUC2.

The intestinal subtype consists of villous architecture with columnar epithelial cells resembling small intestine tissue. It is generally MUC1 negative and MUC2 positive.

The gastric subtype approximates the foveolar epithelium of the stomach and grows in a tubular pattern. It is typically negative for both MUC1 and MUC2.

The oncocytic subtype shows plump cells with eccentrically-placed nuclei and prominently pink cytoplasm. It can show focal positivity for both MUC1 and MUC2.

References

1. Odze and Goldblum, Surgical Pathology of the GI Tract, Liver, Biliary Tract, and Pancreas, Third Ed., 2015.
2. Wan et al. Gallbladder papillary neoplasms share pathological features with intraductal papillary neoplasm of the bile duct. Oncotarget, 2017.
3. Wan et al., Intraductal papillary neoplasm of the bile duct. World J Gastroenterol, 2013.
4. WHO Classification of Tumours Editorial Board, Digestive System Tumours, 5th edition, 2019.