Intraductal papillary mucinous neoplasm (IPMN) of the gastric-type with focal nodular growth of the arborizing papillae: a case of high-grade transformation of the gastric-type IPMN

Acvr1b Loss Increases Formation of Pancreatic Precancerous Lesions From Acinar and Ductal Cells of Origin

BACKGROUND & AIMS

Pancreatic ductal adenocarcinoma can develop from precursor lesions, including pancreatic intraepithelial neoplasia and intraductal papillary mucinous neoplasm (IPMN). Previous studies indicated that loss of Acvr1b accelerates the Kras-mediated development of papillary IPMN in the mouse pancreas; however, the cell type predominantly affected by these genetic changes remains unclear.

METHODS

We investigated the contribution of cellular origin by inducing IPMN associated mutations (KRASG12D expression and Acvr1b loss) specifically in acinar (Ptf1aCreER;KrasLSL-G12D;Acvr1bfl/fl mice) or ductal (Sox9CreER;KrasLSL-G12D;Acvr1bfl/fl mice) cells in mice. We then performed magnetic resonance imaging and a thorough histopathologic analysis of their pancreatic tissues.

RESULTS

The loss of Acvr1b increased the development of pancreatic intraepithelial neoplasia and IPMN-like lesions when either acinar or ductal cells expressed a Kras mutation. Magnetic resonance imaging, immunohistochemistry, and histology revealed large IPMN-like lesions in these mice that exhibited features of flat, gastric epithelium. In addition, cyst formation in both mouse models was accompanied by chronic pancreatitis. Experimental acute pancreatitis accelerated the development of large mucinous cysts and pancreatic intraepithelial neoplasia when acinar, but not ductal, cells expressed mutant Kras and lost Acvr1b.

CONCLUSIONS

These findings indicate that loss of Acvr1b in the presence of the Kras oncogene promotes the development of large and small precancerous lesions from both ductal and acinar cells. However, the IPMN-like phenotype was not equivalent to that observed when these mutations were made in all pancreatic cells during development. Our study underscores the significance of the cellular context in the initiation and progression of precursor lesions from exocrine cells.

Predictive Factors for the Metachronous Development of High-risk Lesions in the Remnant Pancreas After Partial Pancreatectomy for Intraductal Papillary Mucinous Neoplasm

OBJECTIVE

To identify factors predicting the development of high-risk lesions in the remnant pancreas after surgery for intraductal papillary mucinous neoplasm (IPMN).

BACKGROUND

IPMN has unique features, including multifocality, adenoma-carcinoma sequence, and the development of distinct pancreatic ductal adenocarcinoma (PDAC) in the same pancreas. Careful attention should, therefore, be paid to the metachronous occurrence of high-risk lesions, including high-grade dysplasia or invasive carcinoma (HGD/INV) of IPMN and concomitant PDAC in the remnant pancreas after partial pancreatectomy for IPMN.

METHODS

Clinicopathologic and surveillance data for 195 patients who underwent partial pancreatectomy for IPMN were reviewed retrospectively.

RESULTS

Thirteen patients exhibited metachronous development of high-risk lesions including 6 HGD/INV and 7 concomitant PDACs in the remnant pancreas. The 5- and 10-year cumulative incidences of metachronous high-risk lesions in the remnant pancreas were 7.8% and 11.8%, respectively. Twelve of 13 patients had high-risk lesions at the time of initial surgery, and 10 of the 13 IPMNs were located in the distal pancreas. The IPMN subtypes initially resected were gastric in 6 patients, intestinal in 5, and pancreatobililary in the remaining 2. Univariate and multiple regression analyses identified pathologic results of HGD/INV and IPMN located in the distal pancreas as independent predictive factors for metachronous HGD/INV of IPMN, and the pancreatobiliary subtype of IPMN and presence of concomitant PDAC for metachronous PDAC.

CONCLUSIONS

Patients undergoing partial pancreatectomy for IPMN are at high risk of developing lesions requiring surgery in the remnant pancreas, and close, long-term surveillance should be considered in these patients.

A resected case of two branch duct-type intraductal papillary mucinous neoplasms showing different clinical courses after a two-year follow-up

The patient was a 60-year-old man without any particular complaints, but he underwent abdominal computed tomography (CT) and magnetic resonance cholangiopancreatography (MRCP) due to a fatty liver, which revealed two similar cystic lesions regarded as branch duct-type intraductal papillary mucinous neoplasm (BD-IPMN) in the pancreatic body [BD-IPMN (b), 16 mm in size] and tail [BD-IPMN (t), 13 mm in size] without a “high-risk stigmata” or “worrisome features”. He subsequently received follow-up by MRCP every 6 months. Two years later, MRCP showed prominent dilation of the main pancreatic duct (MPD) and mural nodule formation within the dilated MPD adjacent to the BD-IPMN (b). Distal pancreatectomy specimens revealed that the BD-IPMN (b) was lined by low-papillary gastric mucinous epithelium with low-to-intermediate-grade dysplasia and involved the MPD, forming a malignant mural nodule showing pancreatobiliary-type IPMN. In contrast, the BD-IPMN (t) was lined by flat, monolayer columnar gastric mucinous epithelium without atypia, which suggested the possibility of a “simple mucinous cyst”. A genetic analysis showed KRAS mutation only in BD-IPMN (b). Differences in the histological and genetic findings between two similar BD-IPMNs in the present case may suggest what kinds of examinations should be performed in patients with BD-IPMNs without any worrisome features.

Intraductal tubulopapillary neoplasms of the pancreas: case report and review of the literature

A 69-year-old woman was referred to our hospital after incidental identification of a pancreatic mass during follow-up for diabetes mellitus. Various imaging examinations showed a tumor in the main pancreatic duct, without apparent hypersecretion of mucin. Brush cytologic examination revealed class V disease (adenocarcinoma). Because preoperative examination suggested an intraductal neoplasm with associated invasive cancer, total pancreatectomy was performed. Histological examination, based on current World Health Organization classifications, suggested a diagnosis of intraductal tubulopapillary neoplasm. A small cystic lesion adjacent to the intraductal tubulopapillary neoplasm was incidentally diagnosed as serous cystadenoma. The patient has remained well without recurrence as of 24 months postoperatively. Computed tomography and magnetic resonance imaging of the intraductal tubulopapillary neoplasm suggested ductal cell carcinoma of the pancreas rather than intraductal papillary mucinous neoplasm. Distinguishing intraductal tubulopapillary neoplasm from ductal cell carcinoma is clinically important, as intraductal tubulopapillary neoplasm has a favorable prognosis after curative resection.

Carcinogenesis of pancreatic adenocarcinoma: precursor lesions

Pancreatic adenocarcinoma displays a variety of molecular changes that evolve exponentially with time and lead cancer cells not only to survive, but also to invade the surrounding tissues and metastasise to distant sites. These changes include: genetic alterations in oncogenes and cancer suppressor genes; changes in the cell cycle and pathways leading to apoptosis; and also changes in epithelial to mesenchymal transition. The most common alterations involve the epidermal growth factor receptor (EGFR) gene, the HER2 gene, and the K-ras gene. In particular, the loss of function of tumor-suppressor genes has been documented in this tumor, especially in CDKN2a, p53, DPC4 and BRCA2 genes. However, other molecular events involved in pancreatic adenocarcinoma pathogenesis contribute to its development and maintenance, specifically epigenetic events. In fact, key tumor suppressors that are well established to play a role in pancreatic adenocarcinoma may be altered through hypermethylation, and oncogenes can be upregulated secondary to permissive histone modifications. Indeed, factors involved in tumor invasiveness can be aberrantly expressed through dysregulated microRNAs. This review summarizes current knowledge of pancreatic carcinogenesis from its initiation within a normal cell until the time that it has disseminated to distant organs. In this scenario, highlighting these molecular alterations could provide new clinical tools for early diagnosis and new effective therapies for this malignancy.

Diagnostic challenge: intraductal neoplasms of the pancreatobiliary system

To help pathologists avoid misdiagnosis of intraductal neoplasms arising from the pancreatobiliary system, we report two cases that illustrate diagnostic pitfalls. The first is of a 66-year-old man who complained of appetite loss. An early examination led to a diagnosis of intraductal papillary mucinous neoplasm. Macroscopically, a multilocular cyst without visible mucin was identified. Histologically, the compartments consisted of complex fusion of tubular glands surrounded by dilated pancreatic duct. The neoplasm resembled an acinar cell cystadenocarcinoma. However, the neoplastic cells were negative for trypsin. Thus, the final histopathologic diagnosis was an unusual cystic variant of intraductal tubulopapillary neoplasm (ITPN) of the pancreas. The second case is of a 71-year-old man who complained of right upper quadrant pain. Although bile duct stone was suspected, a polypoid nodule was extracted. Histologically, the nodule was composed of tubular glands, with some complex fusion and focal dysplasia, consistent with carcinoma. In addition, lack of MUC-5AC expression led to an initial impression of ITPN of the bile duct. However, the neoplasm showed dysplastic cells based on the columnar cells resembling pyloric glands, indicating the sequential progression. Thus, the final histopathological diagnosis was intraductal papillary neoplasm of the bile duct with high-grade intraepithelial neoplasia. Because phenotypic variants of intraductal neoplasms of the pancreatobiliary system exist, ITPN and ITPN-mimicking tumor must be carefully differentiated from other intraductal neoplasms.

Intraductal papillary mucinous tumors of the pancreas: biology, diagnosis, and treatment

Pancreatic intraductal papillary mucinous neoplasms (IPMNs) rank among the most common cystic tumors of the pancreas. For a long time they were misdiagnosed as mucinous cystadenocarcinoma, ductal adenocarcinoma in situ, or chronic pancreatitis. Only in recent years have IPMNs been fully recognized as clinical and pathological entities, although their origin and molecular pathogenesis remain poorly understood. IPMNs are precursors of invasive carcinomas. When resected in a preinvasive state patient prognosis is excellent, and even when they are already invasive, patient prognosis is more favorable than with ductal adenocarcinomas. Subdivision into macroscopic and microscopic subtypes facilitates further patient risk stratification and directly impacts treatment. There are main duct and branch duct IPMNs, with the main duct type including the intestinal, pancreatobiliary, and oncocytic types and the branch duct type solely harboring the gastric type. Whereas main duct IPMNs have a high risk for malignant progression, demanding their resection, branch duct IPMNs have a much lower risk for harboring malignancy. Patients with small branch duct/gastric-type IPMNs (<2 cm) without symptoms or mural nodules can be managed by periodic surveillance.

A pancreatobiliary-type carcinoma in situ at the periphery of a mural nodule developed from a gastric adenoma in an intraductal papillary mucinous neoplasm

We report a rare case of an intraductal papillary mucinous neoplasm (IPMN) with a pancreatobiliary-type carcinoma in situ (CIS) that originated around a mural nodule formed in a gastric-type adenoma. A 64-year-old man was admitted to our hospital in December 2001 for dilation of the main pancreatic duct, detected on abdominal ultrasonography. Branch-duct-type IPMN (diameter 25 mm) was diagnosed, and because mural nodules were absent, the patient was annually followed up for 5 years. In 2006, computed tomography scans revealed thickening of the tumor wall and the development of a mural nodule (diameter approximately 6 mm); pancreatoduodenectomy with regional lymph-node dissection was performed. Histopathologic examination showed an intraductal papillary mucinous carcinoma arising from an adenoma. Hematoxylin and eosin (H&E) staining revealed that most of the tumor components, including the mural nodule, had adenomatous changes, indicating the tumor to be of the gastric type; however, immunohistochemistry showed positive MUC2 expression. Histologically, the tissues around the nodule, including those showing a cribriform pattern, were diagnosed as CIS. These tissues were classified as the pancreatobiliary-type on the basis of the results of both H&E staining and immunohistochemistry. The patient remained disease-free for 3 years after surgery.

Intraductal oncocytic papillary carcinoma of the pancreas showing numerous hyaline globules in the lumen

Two cases of intraductal oncocytic papillary carcinoma (IOPC) treated surgically were analyzed on light microscopy and immunohistochemistry: that of a 61-year-old man and that of a 55-year-old man. There were no clinical symptoms in either case. Pancreatic abnormalities were discovered incidentally on CT. Various clinical examinations were carried out, and the preoperative diagnosis was intraductal papillary mucinous carcinoma (IPMC) in both cases. Surgery was performed. Macroscopic observation of tissue cross-sections indicated multilocular cystic mass containing polypoid lesions encapsulated by the dilated pancreatic duct. Histologically, the cyst walls were lined by columnar epithelial cells with complex papillary projections associated with oxyphilic cytoplasm, and they were strongly immunoreactive with anti-mitochondrial antibody in the cytoplasm. Electron microscopy showed numerous mitochondria in the cytoplasm. IOPC was diagnosed. Interestingly, amorphous hyaline globules were produced from the oxyphilic cells, which exhibited a bud-like appearance. The hyaline globules were not positive for mucin staining. No case of IPMC with hyaline globules has been reported to date. The production of hyaline globules may be related to oncocytic differentiation. It is suggested that hyaline globules should be regarded as a characteristic of IOPC.

A Case Report of Intraductal Papillary-Mucinous Neoplasm of the Pancreas Showing Morphologic Transformation during Followup Periods

A 64-year-old man underwent MRCP for further examination of gallbladder stones and IPMN of branch-type (IPMN-Br) was pointed out. Yearly MRCP had revealed the gradual increase of the cystic components, marked dilation of the main pancreatic duct (MPD), and filling defects in the MPD. After follow-up for three years, he underwent pancreatoduodenectomy. Histologically, the dilated MPD and connecting dilated branch ducts were filled with nodular growth of tumor cells consisting of gastric-type adenoma with pyloric gland-like structures. In the MPD, a transition from gastric-type adenoma to intestinal-type carcinoma was observed. In addition, in a dilated branch duct, some components of intestinal-type carcinoma with marked arborizing structures were observed. A minimally invasion was observed around branch ducts. Immunohistochemistry revealed diffuse nuclear accumulation of PCNA and Ki67 in the tumor cells of branch dusts. Our observations suggest that the secondary infiltration to the MPD of IPMN-Br and IPMN-Br possesses malignant potential for microinvasion.

Cystic neoplasms of the exocrine pancreas

The increasing use of radiological imaging has led to greater detection of small and asymptomatic cystic lesions of the pancreas. Most are resectable, but not all are neoplastic. This review provides an update on the histopathology, immunohistochemistry, molecular biology, pathogenesis and management of cystic neoplasms of the exocrine pancreas. These include the serous, the mucinous cystic, the intraductal papillary mucinous and the solid pseudopapillary neoplasms. Recently reported variants are described and very rare cystic variants of other pancreatic epithelial and mesenchymal neoplasms are briefly mentioned.

Pancreatic intraductal papillary-mucinous neoplasms: a new and evolving entity

For a long time, intraductal tumors of the pancreas were neglected because they were misdiagnosed as mucinous cystadenocarcinoma, ordinary ductal adenocarcinoma, or chronic pancreatitis. Only in recent years have they been recognized as clinical and pathological entities. Most common are the intraductal papillary-mucinous neoplasms. Although they show an adenoma-carcinoma sequence, they have proved to have a more favorable prognosis than ductal adenocarcinoma, when resected in a preinvasive state. Recently, it has become clear that they constitute a heterogeneous group with at least four subtypes. Their stratification reveals that the various intraductal papillary-mucinous neoplasm subtypes have different biological properties with different prognostic implications.