Molecular Analysis of an Intestinal Neuroendocrine/Non-neuroendocrine Neoplasm (MiNEN) Reveals MLH1 Methylation-driven Microsatellite Instability and a Monoclonal Origin: Diagnostic and Clinical Implications

Clinical and Genomic Characterization of Pancreatic Ductal Adenocarcinoma with Signet-Ring/Poorly Cohesive Cells

Signet-ring cell (SRC)/poorly cohesive cell carcinoma is an aggressive variant of pancreatic ductal adenocarcinoma (PDAC). This study aimed to clarify its clinicopathologic and molecular profiles based on a multi-institutional cohort of 20 cases. The molecular profiles were investigated using DNA and RNA sequencing. The clinicopathologic parameters and molecular alterations were analyzed based on survival indices and using a validation/comparative cohort of 480 conventional PDAC patients. The primary findings were as follows: (1) clinicopathologic features: SRC carcinomas are highly aggressive neoplasms with poor prognosis, and the lungs are elective metastatic sites; (2) survival analysis: a higher SRC component was indicative of poorer prognosis. In particular, the most clinically significant threshold of SRC was 80%, showing statistically significant differences in both disease-specific and disease-free survival; (3) genomic profiles: SRC carcinomas are similar to conventional PDAC with the most common alterations affecting the classic PDAC drivers KRAS (70% of cases), TP53 (55%), SMAD4 (25%), and CDKN2A (20%). EGFR alterations, RET::CCDC6 fusion gene, and microsatellite instability (3 different cases, 1 alteration per case) represent novel targets for precision oncology. The occurrence of SMAD4 mutations was associated with poorer prognosis; (4) pancreatic SRC carcinomas are genetically different from gastric SRC carcinomas: CDH1, the classic driver gene of gastric SRC carcinoma, is not altered in pancreatic SRC carcinoma; (5) transcriptome analysis: the cases clustered into 2 groups, one classical/exocrine-like, and the other squamous-like; and (6) SRC carcinoma-derived organoids can be successfully generated, and their cultures preserve the histologic and molecular features of parental SRC carcinoma. Although pancreatic SRC carcinoma shares similarities with conventional PDAC regarding the most important genetic drivers, it also exhibits important differences. A personalized approach for patients with this tumor type should consider the clinical relevance of histologic determination of the SRC component and the presence of potentially actionable molecular targets.

Microsatellite instability in pancreatic and ampullary carcinomas: histology, molecular pathology, and clinical implications

Microsatellite instability (MSI)/defective DNA mismatch repair (dMMR) represents an important molecular alteration with diagnostic, prognostic, and predictive value. The increasing interest toward this genetic alteration is given to the high response rate of MSI/dMMR tumors to immunotherapy. There are different cancers in the periampullary region that can harbor MSI/dMMR, and significant morphological-molecular correlates should be acknowledged in this district: (1) pancreatic ductal adenocarcinoma (PDAC): in this tumor category, the prevalence of MSI/dMMR is about 1-2%, and medullary and colloid variants are the most typically involved; (2) ampullary adenocarcinoma: here the prevalence of MSI/dMMR is up to 18%, and in this neoplastic group, MSI/dMMR is more commonly found in the intestinal subtype; (3) pancreatic acinar cell carcinoma: here the prevalence of MSI/dMMR is up to 14%; and (4) pancreatic and ampullary neuroendocrine carcinoma: in this tumor category, the prevalence of MSI/dMMR is up to 5-8%, and this molecular alteration should be assessed also in cases of mixed neuroendocrine-non-neuroendocrine neoplasms. Given the clinical importance of MSI/dMMR and its not-negligible prevalence among the different carcinomas arising in this district, its assessment should become part of the routine diagnostic workflow at least for the most typical histotypes. The test of choice is represented by immunohistochemistry for PDAC and ampullary carcinomas, and by direct molecular analyses including MSI-based polymerase chain reaction and next-generation sequencing for acinar cell and neuroendocrine carcinomas.

From morphology to molecular targets—the pathologist’s view in diagnosing gastroenteropancreatic neuroendocrine neoplasms

In the last decade, a number of genetic alterations in gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) have been identified. In addition, differences in tumor morphology as well as proliferation index (Ki-67) or number of mitoses have led to changes in the classification of these neoplasms. According to the new World Health Organization (WHO) classification, GEP-NENs are now divided into two genetically and prognostically different categories: (i) well-differentiated neuroendocrine tumors (NET) subdivided into low (G1), intermediate (2) and high (G3) grade tumors, and (ii) poorly differentiated neuroendocrine carcinomas (NEC). In addition, a group of mixed neuroendocrine–non-neuroendocrine neoplasms (MiNEN) has been defined. This review focuses on the clinical, morphological, immunohistochemical and molecular findings of the GEP-NENs and their key diagnostic features that can help the pathologist to differentiate between tumors in this heterogeneous group. In challenging cases, additional immunohistochemical and/or molecular analysis can be helpful to determine the correct diagnosis and proper treatment for the patient.

Mixed neuroendocrine–nonneuroendocrine neoplasms of the gastrointestinal system: An update

Mixed neuroendocrine-nonneuroendocrine neoplasms (MiNENs) of the digestive tract are a rare heterogeneous group of tumors that present many challenges in terms of diagnosis and treatment. Over the years, the diagnostic criteria, classification, and clinical behavior of these tumors have been the subjects of ongoing debate, and the various changes in their nomenclature have strengthened the challenges associated with MiNENs. This review is performed to provide an understanding of the key factors involved in the evolution of the designation of these tumors as MiNEN, highlight the current diagnostic criteria, summarize the latest data on pathogenesis and provide information on available treatments. Moreover, this work seeks to increase the awareness about these rare neoplasms by presenting the clinicopathological features and prognostic factors that play important roles in their behavior and discussing their different regions of origin in the gastrointestinal system (GIS). Currently, the MiNEN category also includes tumors in the GIS with a nonneuroendocrine component and epithelial tumors other than adenocarcinoma, depending on the organ of origin. Diagnosis is based on the presence of both morphological components in more than 30% of the tumor. However, this value needs to be reconfirmed with further studies and may be a limiting factor in the diagnosis of MiNEN by biopsy. Furthermore, available clinicopathological data suggest that the inclusion of amphicrine tumors in the definition of MiNEN is not supportive and warrants further investigation. The diagnosis of these tumors is not solely based on immunohistochemical findings. They are not hybrid tumors and both components can act independently; thus, careful grading of each component separately is required. In addition to parameters such as the metastatic state of the tumor at the time of diagnosis and the feasibility of surgical resection, the aggressive potential of both components has paramount importance in the choice of treatment. Regardless of the organ of origin within the GIS, almost MiNENs are tumors with poor prognosis and are frequently encountered in the elderly and men. They are most frequently reported in the colorectum, where data from molecular studies indicate a monoclonal origin; however, further studies are required to provide additional support for this origin.