Intracholecystic Tubular Nonmucinous Neoplasm of the Gallbladder

Intracholecystic neoplasms (ICNs) of gallbladder are a challenging and relatively poorly understood family of tumors. Recently, a distinct category of ICNs, characterized by pedunculated polyps composed of lobules of back-to-back small tubular/acinar units lined by minimally mucinous or nonmucinous cells, has been found to be biologically, behaviorally, and molecularly different from other ICNs, and termed intracholecystic tubular nonmucinous neoplasm (ICTN).

To review the clinicopathologic characteristics of ICTN of the gallbladder.

This review is based on the literature and the author's own research.

ICTNs, initially recognized by their distinctive morphology and growth pattern, have distinct clinicopathologic characteristics. They are unlikely to be diffuse and multifocal like ordinary intracholecystic papillary neoplasms (ICPNs), and they do not appear to confer the field risk that ICPNs do. Instead, they form solitary pedunculated polyps (and often appear as detached debris in the lumen) and occur in the background of uninvolved gallbladder. In fact, they appear to be arising in cholesterol polyps. By morphology and MUC6 expression they resemble pancreatic/biliary intraductal tubulopapillary neoplasms, and they have been also called "complex nonmucinous pyloric gland adenomas" in the past. Although their complexity warrants the diagnosis of high-grade dysplasia/carcinoma in situ (and they have been typically diagnosed as "tubular adenocarcinoma" in Asia and South America), ICTNs are invasion resistant, with no documented invasive carcinoma developing within this lesion to date. The presence of morules, which display nuclear β-catenin expression, places this lesion in the so-called BROCN family of tumors, which are believed to be hormonally driven. Further molecular studies are needed to explore the roots of their behavior.