The pancreas is a solid organs with a three-dimensional (3D) cellular structure, where cell-to-cell interactions could play key roles in organ development, homeostasis and regeneration as well as diseases including tumorigenesis. To understand the mechanisms underlying those processes, it is important to investigate signaling pathways not only within cells but also between cells.

Recent advances in experimental techniques including a 3D culture system, Cre/loxP-based genetic lineage tracing and cell ablation models, have allowed us to explore cell-to-cell communications, leading to an improved understanding of tissue behaviors as a cell population. We present recent reeslts to provide a brief overview of intercellular crosstalk in the pancreas.

Exome sequence analysis of patient tissues have identified specific mutations in intraductal papillary mucinous neoplasm (IPMN), such as GNAS and KLF4, suggesting that IPMN may have a distinctive progression pathway compared to pancreatic intraepithelial neoplastic lesion, a preneoplastic lesion of conventional pancreatic ductal adenocarcinoma (PDAC). Many topics remain to be resolved in IPMN, including the mechanism by which they imitate various gastrointestinal histologies, such as gastric or intestinal tissues. The biological differences among IPMN derived cancer, conventional PDAC, and IPMN concomitant cancer are an important issue.

Therefore, we have been elucidating the characteristics of IPMN with the hope of finding IPMN lineage specific therapeutic targets. To achieve this, we have established series of patient-derived organoids from IPMN and IPMN cancers, for which human models have been limited so far. This enabled us to thoroughly apply a wide range of cutting-edge genomic and epigenomic sequencing techniques in IPMN together with phenotyping their vulnerabilities. We discovered that IPMN lineages have distinct epigenomic profiles with characteristic addictive biological behaviors supported by MNX1-HNF1B axis, implying the feasibility of therapeutic implementation. We present the unique biology of IPMN with future research perspectives.

Biomarkers are essential for the early detection of pancreatic cancer, which has few subjective symptoms. Delayed detection of pancreatic cancer is associated with increased mortality due to its often rapid dissemination. Currently, the development of cancer screening tests a using liquid biopsy is underway worldwide, and some testing methods are now covered by the national health insurance system in Japan. There are several materials that can be analyzed by liquid biopsy. Exosomes, secreted by cells, are attracting attention as a new target for liquid biopsy. In this paper, we introduce some examples of exosome-based liquid biopsies, which analyze and detect molecules contained in exosomes from blood and other fluids for diagnosis, mainly from the viewpoint of early diagnosis, and outline the potential for exosomes in the diagnosis of pancreatic cancer.

Pancreatic cancer is characterized by an abundant desmoplastic stroma. Emerging evidence based on current technology, including single-cell transcriptomics, indicates that cancer-associated fibroblasts (CAFs) in human pancreatic cancer are phenotypically and functionally more heterogeneous than previously thought. Utilizing multiplex immunohistochemistry, we recently identified two mutually exclusive fibroblast subtypes defined by expression levels of α smooth muscle actin (αSMA) and fibroblast activation protein α (FAP) within pancreatic cancer tissues. In situ quantitative analyses of these fibroblast subtypes and collagen using formalin-fixed paraffin-embedded slides from 215 patients with treatment naïve pancreatic cancers manifested three distinct stroma types associated with differing prognoses and molecular pathological features. We introduce a multiplex image analysis-based quantitative system and discuss ①transcriptomic differences between the three pancreatic cancer stroma types and ②differences between non-tumor fibrosis and tumor-associated desmoplasia from the viewpoint of stromal composition of fibroblast subtypes and collagen.

One characteristic of pancreatic cancer, considered incurable, is fibrosis in the interstitium and associated tissue sclerosis. Tissue stiffness is known to induce increased intrastromal pressure and vascular collapse, inhibiting the penetration of anticancer drugs into the interstitium with delivery to cancer cells. Cancer-associated fibroblasts (CAFs) play a central role in the development of fibrosis in the stroma. Various therapies targeting CAFs have been developed but have not yet been successful. In this study, we demonstrated that inducing the expression of Meflin, a marker and functional molecule of tumor suppressive CAFs, in CAFs improves the sensitivity to chemotherapy of pancreatic cancer. Furthermore, a compound library screening revealed that AM80, a synthetic retinoid, effectively induces the expression of Meflin in CAFs and improves sensitivity to chemotherapy with improved drug delivery. Based on these results, the authors are conducting a clinical trial of AM80 in combination with conventional anticancer agents to treat patients with unresectable pancreatic cancer to evaluate the efficacy of AM80.

Conventional histopathological evaluation can only view arbitrary cross sections of a histologic specimen. However, recently, it is possible to observe the entire specimen using tissue clearing technology with three-dimensional imaging. If the entire specimen can be evaluated, the three-dimensional structure of the tissue is observed. As a result, there are benefits such as fewer missed lesions and the clarification of new pathologic entities. There are dozens of tissue clearing reagents available. Each reagent and microscope has its own characteristics. It is important to select the appropriate reagent and microscope according to the intended purpose. Tissue clearing technology is reviewed in this paper. The evaluation of Pancreatic Neuroendocrine Neoplasms by tissue clearing technology with three-dimensional imaging is introduced.

To clarify the histological features and utility of immunostaining, 83 autopsy cases, 15 cases of obstructive pancreatitis, and eight cases of tumefactive chronic pancreatitis were analyzed histologically and immunohistochemically for CD56 and cytokeratin 19 (CK19). Acinar ductal metaplasia (ADM) was identified in 50 autopsy cases (60%), all cases (100%) of obstructive pancreatitis, and seven cases (88%) of chronic pancreatitis. In lesions with ADM, the typical purple color in the normal pancreatic tissue was diminished, and microcystic structures that looked like dilated acinar lumens (notable in the autopsy cases) and small duct-like structures (notable in the cases of obstructive pancreatitis) were observed. ADM in the autopsy cases contained protein plugs, and degree of ADM formation correlated with fat necrosis (P < 0.001) or inflammatory cell infiltration (P = 0.002), indicating that ADM is a reflection of acinar cell injury. ADM was diffusely positive for CD56. CD56 expression in ADM was more specific than CK19, which was also expressed in the intercalated ducts and centroacinar cells, and is a useful immunohistochemical marker.

Recently, the Japanese clinical diagnostic criteria for autoimmune pancreatitis (AIP) 2018 (JPS2018), a revision of the JPS2011, have been published. The present study aimed to clarify the diagnostic rate and issues regarding the JPS2018 by comparing results with the JPS2011 and International Consensus Diagnostic Criteria (ICDC). The diagnostic rates for type 1 AIP (definitive and probable AIP) in the JPS2018, JPS2011, and ICDC were 91%, 83.4%, and 87.6%, respectively. One reason why the diagnostic rate for JPS2018 improved was the establishment of a new procedure that includes magnetic resonance cholangiopan-creatography (MRCP) and endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) biopsy in the JPS2018. It was impossible to diagnose 6 patients undergoing pancreatic resection as having AIP based on preoperative information including radiological and serological findings. The histological diagnosis based on EUS-FNA biopsy tissues is required for further improvement of the diagnostic rate for AIP.

A 42-year-old man presented with appetite-loss, abdominal discomfort and weight-loss. Enhanced CT scan revealed a tumor in the pancreatic head, hepatic hilar lymphadenopathy and a liver tumor with a final diagnosis of pancreatic carcinoma with liver metastasis and lymph node metastasis (T3N1M0 Stage IV). There was obstructive jaundice due to hilar adenopathy. Endoscopic drainage was performed for obstructive jaundice which led to resolution of jaundice and hospital discharge. Ten days later he presented with upper abdominal pain. Enhanced CT scan showed rupture of a liver metastasis from pancreatic carcinoma. Emergency transcatheter arterial embolization was performed to control bleeding. Chemotherapy was administered after bleeding was controlled. Rupture of metastatic liver lesions are rare, and there are only five previous reports of ruptured lesions from pancreatic cancer. In the present patient, there was a rapid increase in the liver metastasis, and blood vessel collapse due to increased intratumor pressure was suspected.

Patients with pancreatic ductal adenocarcinoma concomitant with IPMN-derived carcinoma are rare. We report a 75-year-old male patient followed-up for IPMN for seven years. The main pancreatic duct (MPD) at the pancreatic head was narrowed and the MPD at the pancreatic tail was noted to be dilated by MRCP. CT scan, MRI and EUS did not reveal tumor. Therefore, the patient underwent endoscopic retrograde cholangiopancreatography, and malignant cells were detected by cytology. Since malignant cells were detected in the head and tail of the pancreas, total pancreatectomy was performed. Pathology results revealed concomitant pancreatic ductal adenocarcinoma in the head of pancreas and IPMN-derived carcinoma in the tail of the pancreas. The patient was diagnosed with pancreatic cancer T1aN0M0 Stage IA with changes in the main pancreatic duct.