Intracholecystic papillary-tubular neoplasms (ICPN) of the gallbladder (neoplastic polyps, adenomas, and papillary neoplasms that are ≥1.0 cm): Clinicopathologic and immunohistochemical analysis of 123 cases

The literature on the clinicopathologic characteristics of tumoral intraepithelial neoplasms (neoplastic polyps) of the gallbladder (GB) is fairly limited, due in part to the variability in definition and terminology. Most reported adenomas (pyloric gland type and others) were microscopic and thus regarded as clinically inconsequential, whereas papillary in situ carcinomas have been largely considered a type of invasive adenocarcinoma under the heading of "papillary adenocarcinomas." In this study, 123 GB cases that have a well-defined exophytic preinvasive neoplasm measuring ≥1 cm were analyzed. The patients were predominantly female (F/M=2:1) with a mean age of 61 y and a median tumor size of 2.2 cm. Half of the patients presented with pain, and in the other half the neoplasm was detected incidentally. Other neoplasms, most being gastrointestinal tract malignancies, were present in 22% of cases. Gallstones were identified in only 20% of cases. Radiologically, almost half were diagnosed as "cancer," roughly half with polypoid tumor, and in 10% the lesion was missed. Pathologic findings: (1) The predominant configuration was papillary in 43%, tubulopapillary in 31%, tubular in 26%. (2) Each case was assigned a final lineage type on the basis of the predominant pattern (>75% of the lesion) on morphology, and supported with specific immunohistochemical cell lineage markers. The predominant cell lineage could be identified as biliary in 50% (66% of which were MUC1), gastric foveolar in 16% (all were MUC5AC), gastric pyloric in 20% (92% MUC6), intestinal in 8% (100% CK20; 75% CDX2; 50%, MUC2), and oncocytic in 6% (17% HepPar and 17% MUC6); however, 90% of cases had some amount of secondary or unclassifiable pattern and hybrid immunophenotypes. (3) Of the cases that would have qualified as "pyloric gland adenoma," 21/24 (88%) had at least focal high-grade dysplasia and 18% had associated invasive carcinoma. Conversely, 8 of 47 "papillary adenocarcinoma"-type cases displayed some foci of low-grade dysplasia, and 15/47 (32%) had no identifiable invasion. (4) Overall, 55% of the cases had an associated invasive carcinoma (pancreatobiliary type, 58; others, 10). Factors associated significantly with invasion were the extent of high-grade dysplasia, cell type (biliary or foveolar), and papilla formation. Among systematically analyzed invasive carcinomas, tumoral intraepithelial neoplasia was detected in 6.4% (39/606). (5) The 3-year actuarial survival was 90% for cases without invasion and 60% for those associated with invasion. In contrast, those associated with invasion had a far better clinical outcome compared with pancreatobiliary-type GB carcinomas (3-yr survival, 27%), and this survival advantage persisted even with stage-matched comparison. Death occurred in long-term follow-up even in a few noninvasive cases (4/55; median 73.5 mo) emphasizing the importance of long-term follow-up. In conclusion, tumoral preinvasive neoplasms (≥1 cm) in the GB are analogous to their pancreatic and biliary counterparts (biliary intraductal papillary neoplasms, pancreatic intraductal papillary mucinous neoplasms, and intraductal tubulopapillary neoplasms). They show variable cellular lineages, a spectrum of dysplasia, and a mixture of papillary or tubular growth patterns, often with significant overlap, warranting their classification under 1 unified parallel category, intracholecystic papillary-tubular neoplasm. Intracholecystic papillary-tubular neoplasms are relatively indolent neoplasia with significantly better prognosis compared with pancreatobiliary-type GB carcinomas. In contrast, even seemingly innocuous examples such as those referred to as "pyloric gland adenomas" can progress to carcinoma and be associated with invasion and fatal outcome.