Pathological characterization of intracholecystic papillary neoplasm: A recently proposed preinvasive neoplasm of gallbladder

Intracholecystic papillary neoplasm (ICPN) is a recently proposed gallbladder neoplasm. Its prevalence and pathologies remain to be clarified. A total of 38 ICPN cases (28 ICPNs identified among 1904 cholecystectomies (1.5%) and in 100 surgically resected primary gallbladder neoplasms (28%) in Fukui Prefecture Saiseikai Hospital, Japan, and other 10 ICPNs) were examined pathologically and immunohistochemically. They were composed of 21 males and 17 females with a mean age of 75 years old, and presented intraluminal growth of papillary lesions with fine fibrovascular stalks. ICPNs were relatively frequent in the fundus (n = 11) and body (n = 9). Grossly, the conglomerated sessile type (n = 30) was more frequent than the isolated polypoid type (n = 8). All cases were classified as high-grade dysplasia, and they were further divided into 22 cases presenting irregular structures and 16 cases presenting regular structures. The former showed frequent complicated lesions and stromal invasion (54.5%) compared to the latter (12.5%). Twenty-four cases showed predominantly either of four subtypes (11 gastric, 7 intestinal, 4 biliary and 2 oncocytic subtype), while the remaining14 cases showed mixture of more than two subtypes. In conclusion, ICPN presented unique preinvasive neoplasm with characteristic histopathologies. Irregular histologies and complicated lesions of ICPN were related to stromal invasion. •Gallbladder cancer develops from preinvasive lesions such as intracholecystic papillary neoplasm.•Intracholecystic papillary neoplasm is a recently proposed preinvasive lesion and is said to be rare.•Regular/non-complicated type and irregular/complicated type are recognizable in intracholecystic papillary neoplasm.•Irregular/complicated type of intracholecystic papillary neoplasm is likely followed by stromal invasion of neoplasm.