A list of interactive microscopy courses that will be held at the 2026 Annual Meeting is below.

Bone and Soft Tissue

Benign and Malignant Giant Cell-Rich Lesions: An Overview and a Practical Approach

Faculty: Carina Dehner, MD, PhD, Indiana University School of Medicine

Professional Practice Gap: 

Giant cell-rich lesions may involve bone and soft tissue and comprise a heterogenous group of reactive and neoplastic processes with variable clinical behavior. Diagnosis entirely based on histologic examination is often challenging and, in addition to clinical and radiographic correlation, the use of immunohistochemistry and/or molecular testing is limited in its capability of helping to distinguish certain neoplasms from another. Additionally, molecular advances have led to the recognition of several new entities, some of which may benefit from novel therapeutic approaches.  Given the small volume of such cases, the experience and confidence level of the pathologist may be limited. This session will provide an overview of the most important diagnoses not to miss as well as introduce some of the novel and emerging entities. Topics to be discussed for each entity are potential pitfalls, differential diagnoses and useful immunohistochemical and molecular studies that may help diagnosis.

Learning Objectives:

  1. Recognize the most important benign and malignant giant cell-rich neoplasms and understand the correlation with clinical and radiographic correlation.
  2. Recognize some of the non-neoplastic mimickers of said tumors.
  3. Know some of the more recently described entities.
  4. Know the available immunohistochemical and molecular tests to aid in diagnosis.
Breast Pathology

Mimicry is the Highest Form of Flattery: Malignant and Benign Mimics in Breast Pathology (Round 2)

Faculty: Erinn Downs, DO, Mayo Clinic Arizona

Professional Practice Gap:

In the breast, there can be histologic overlap among lesions that are biologically benign and those that may have a more aggressive behavior with either local recurrence or even the potential to metastasis. This occurs as some benign lesions, including inflammatory and reactive processes, may mimic an invasive carcinoma, both on breast imaging as well as in their histologic appearance. At the same time, there are some malignant lesions that may appear banal. Couple these lesions that may overlap histologically along with the rarity of finding them within the breast, and the diagnoses become even more challenging. False positive breast cancer diagnosis rates (benign disease being diagnosed as malignant) vary depending on the specimen type assessed. When considering core needle biopsies, the false positive rate ranges from 0.25%-2.4%, while for surgically excised specimens the false positive rate ranges from 0.67%-1.2%.   False negative rates (the lesion is not appreciated) have also been studied and similarly show a rate of roughly 1.8%. Although the overall percentage of misclassified cases is seemingly low, this misclassification may lead to over or under treatment, in addition to adding significant psychologic stress for the patient.

Learning Objectives:

  1. Recognize the diagnostic overlap of some lesions identified in the breast and develop a consistent approach to arriving at the correct diagnosis.
  2. Appreciate the spectrum of differing biologizes in entities that have histologic overlap.
  3. Describe the ancillary studies that can aid in establishing the diagnosis, while acknowledging the limitations of these ancillary studies.



Effusions: Approach, Ancillary Studies, and Pitfalls

Faculty: Judy Pang, MD, University of Michigan

Professional Practice Gap:

There is significant overlap in cytomorphology of benign reactive and malignant effusions.  Clinical and radiologic correlation is essential in avoiding both false negative and false positive interpretations.  Given that these slides are screened by cytotechnologists, it is not infrequent that pathologists evaluate these specimens without reviewing clinical history. This session will attempt to provide a practical approach to the evaluation of effusion cytology specimens, walking the participant through the thought process in a stepwise fashion utilizing actual slides including ThinPrep, Diff-quik smears, cell block, and/or Giemsa cytospins.  Topics to be addressed include potential pitfalls, understanding the pertinent positives and negatives in clinical history, and knowing when immunostains are needed.  The importance of discussions with hematopathology colleagues and clinical teams will also be highlighted.

Learning Objectives:

  1. Articulate the pertinent positives and negatives in clinical history when assessing an effusion cytology specimen.
  2. Explain what immunostains are needed and in what clinical scenario immunostains would be warranted to avoid a false negative interpretation.
  3. Describe some potential pitfalls leading to false positive interpretations.
  4. Specify when discussions with clinical team or hematopathology colleagues are indicated.


Gastrointestinal Pathology

The Food Pipe is Ripe with Problematic Inflammatory and Premalignant Lesions: The Importance of Clinical and Endoscopic Correlation in Pathologic Reporting

Faculty: James Mitchell, MD, UT Southwestern Medical Center

Professional Practice Gap:

Accurate assessment of esophageal pathologies is important for clinical management. However, many forms of esophageal injury have significant overlapping features requiring correlation with clinical parameters including but not limited to endoscopic findings, immune status, history of caustic exposure, and medication administration. Despite recent developments in pattern-based approaches to injury, many esophageal lesions remain diagnostically challenging, especially if the pathologist is not familiar with pertinent histopathologic, clinical, and endoscopic findings.  Precise pathologic reporting with useful commentaries to include appropriate differential diagnoses can be essential for further management.

Learning Objectives:

  1. Characterize the endoscopic and histomorphologic findings of inflammatory and premalignant lesions of the esophagus
  2. Apply a pattern-based approach to the various forms of esophageal injury to generate appropriate differential diagnoses
  3. Provide useful commentary in pathologic reporting to guide clinical management when key clinical paraments are not available


Appendiceal Pathology: Tips, Tricks, and Traps

Faculty: Krutika Patel, MD, MBBS, Vanderbilt University Medical Center

Professional Practice Gap:

Appendiceal specimens are one of the most common gastrointestinal specimens and encompass a spectrum of lesions including inflammatory, benign, and malignant tumors. Some benign appendiceal lesions are relatively uncommon, can mimic mucinous tumors, and are difficult to diagnose. Post-inflammatory mucosal hyperplasia and appendiceal diverticulosis simulate mucinous neoplasms, causing diagnostic confusion. Distinction between neoplasia and its mimics is particularly important since many appendiceal mucinous neoplasms have malignant potential. Some neoplastic processes in the appendix have histological similarity to their colonic counterparts, and recognition of some these neoplasms is relatively straightforward. However, low-grade appendiceal mucinous neoplasms (LAMNs) are unique tumors of the appendix that can spread beyond the appendix into the peritoneal cavity. The disease course is variable and critically dependent on the extent of disease spread at presentation. However, diagnosis of these neoplasms is challenging and fraught with confusing terminology and numerous classification systems. Recently, progress has been made in understanding the underlying biology and clinical course of LAMNs and in establishing consensus guidelines for diagnostic terminology and reporting. We will review the current terminology, grading, and staging of appendiceal mucinous neoplasms, with an emphasis on common challenging scenarios as well as practical approaches to handling these cases. This case-based review course will provide guidance on accurately diagnosing LAMNs and their benign mimickers. The faculty will include discussions on the clinical significance of each diagnosis, as well as tips for gross examination and sampling.

Learning Objectives:

  1. Identify the morphologic diagnostic criteria of a variety of common and uncommon benign and malignant lesions of the appendix
  2. Recognize overlapping and distinct features of entities in the differential diagnosis and undertake additional workup and/or purse relevant clinical correlation to render an accurate diagnosis
  3. Describe updated consensus terminology and classification of low- and high-grade appendiceal mucinous neoplasms, and recognize the challenges in staging of appendiceal mucinous neoplasms and be cognizant of the recent updates
  4. Understand the morphologic features of non-neoplastic mucinous hyperplasia, and post inflammatory changes to facilitate their distinction from low-grade appendiceal mucinous neoplasms


Demystifying Diverse Patterns of Colonic Mucosal Injury: Above and Beyond Idiopathic Inflammatory Bowel Disease

Faculty: Dipti Karamchandani, MD, UT Southwestern Medical Center

Professional Practice Gap:

With escalating endoscopic procedures, pathologists are seeing an increased number of colonic biopsies retrieved for histologic assessment. Our clinicians rely upon pathology reports to guide them towards the possible or definite etiology for further patient management. Hence, it is crucial for pathologists to deliver a comprehensive and precise pathology report that can speak clearly to clinical colleagues. Identification of the pattern of injury in colonic biopsies is the first step towards delineating an etiology, as every pattern of injury has its own set of histologic differential diagnosis.  In most cases, these can be narrowed down to the accurate diagnosis by looking for certain characteristic histomorphologic clues with or without additional ancillary testing, and by correlation with clinical history and laboratory data. This session will attempt to cover the various histologic patterns of mucosal injury (e.g. active colitis, chronic active colitis, microscopic colitis, apoptotic colopathy, ischemic colitis, mixed patterns of injury), along with histopathologic differentials and how to correlate these features with clinical history and ancillary testing to narrow down the differential diagnosis.

Learning Objectives:

  1. Identify different patterns of mucosal injury seen in colonic biopsies (i.e. active colitis, chronic active colitis, microscopic colitis, ischemic colitis, apoptotic colopathy, mixed pattern).
  2. Discuss the differentials for each histologic pattern of colonic injury encountered in mucosal biopsies.
  3. Correlate the histologic findings with clinical history and ancillary testing to narrow down the differential and to clinch the final diagnosis.
Genitourinary Pathology

The Malady with a Thousand Faces: Urothelial Carcinoma and Its Morphological Subtypes

Faculty: Mahmut Akgul, MD, Albany Medical Center

Professional Practice Gap:

Urothelial carcinoma is the most common malignancy arising from the urinary tract. A substantial number of cases, along with its “conventional” histologic features, exhibit morphologic subtypes. The recent 5th edition of the World Health Organization (WHO) classification on urinary tract tumors describes 14 different subtypes (squamous, glandular, trophoblastic, nested, large nested, tubular and microcystic, micropapillary, lymphoepithelioma-like, plasmacytoid, giant cell, lipid rich, glycogen rich, sarcomatoid, poorly differentiated). High-grade neuroendocrine tumors (i.e. small cell carcinoma) can also be seen, usually mixed with conventional and variant urothelial carcinoma, but are not formally addressed. Moreover, there are few other subtypes that have been identified in the literature although not specifically discussed in the WHO (e.g. pseudoangiosarcomatous, chordoid, hepatoid, yolk sac). While some of the subtypes, such as urothelial carcinoma with squamous or glandular differentiation are relatively more common and well-recognized, many of these subtypes are infrequent and less appreciated, which may cause diagnostic challenge and misinterpretation as non-neoplastic lesions or non-urothelial neoplasms. The recent International Society of Urologic Pathology (ISUP) Consensus Conference on Current Issues in Bladder Cancer has highlighted the importance of identifying urothelial carcinoma subtypes, regardless of their extent within the entire biopsy/resection specimen. Although all urothelial carcinoma subtypes are currently considered high-grade tumors, accurate documentation is critical in predicting the outcomes and optimal management in patients with “variant histology” urothelial carcinoma.

Learning Objectives:

  1. Properly identify urothelial carcinoma subtypes and to report regardless of the percentage
  2. Understand non-urothelial and/or non-neoplastic lesions that may be confused with urothelial carcinoma variants
  3. Provide evidence-based recommendations on how to accurately diagnose urothelial carcinoma variants in challenging situations


Spindle Cell Lesions Involving Genitourinary Organs

Faculty: Liwei Jia, MD, PhD, UT Southwestern Medical Center

Professional Practice Gap:

A variety of spindle cell neoplasms occur in genitourinary organs, which includes benign and malignant tumors. Among them, inflammatory myofibroblastic tumors are clinically indolent. On the other hand, certain other lesions such as sarcomatoid carcinomas are typically highly aggressive. Diagnostic accuracy is essential for this group of patients to receive proper clinical management. However, these lesions may pose significant diagnostic difficulties, due to the rarity, and overlapping morphology and immunophenotypic features. These important diagnostic dilemmas have resulted in numerous articles, including research and review papers (PMID: 26834412, 11598176, 18941404, 17509394, 19912355). Increasing the awareness of diagnostic dilemmas, particularly emphasis on associated clinical implications, would be beneficial to practicing pathologists. Surgical pathologists should be aware of potential pitfalls and consider a broad differential diagnosis for spindle cell lesions in genitourinary organs.

Learning Objectives:

  1. Recognize the key morphologic features to formulate proper differential diagnosis for sarcomatoid genitourinary entities
  2. Develop an integrated diagnostic approach to sarcomatoid genitourinary entities
  3. Learn about the clinical behavior and biology of the entities
  4. Understand the clinical implications for these sarcomatoid genitourinary entities


Gynecologic Pathology

Uterine Mesenchymal Tumors Demystified: A Guide to Well-Established and Recently Described Entities

Faculty: David Kolin, MD, PhD, Brigham and Women’s Hospital

Professional Practice Gap:

Uterine mesenchymal neoplasia includes a wide range of tumors, and the number of recently described entities has exploded over the past several years. Accurate diagnosis of these tumors is critical because the prognosis varies between them, and some tumors have specific targeted treatments available. However, these tumors are uncommonly encountered in general practice, and most pathologists are not comfortable working up or diagnosing them.

Learning Objectives:

  1. Formulate a diagnostic approach to uterine mesenchymal tumors
  2. Describe morphologic, immunohistochemical, and molecular features of both well-known and recently described uterine sarcomas
  3. Suggest appropriate ancillary studies for diagnostic, prognostic, and predictive indications


Head & Neck Pathology

It’s All in Your Head (and Neck): Unusual and Challenging Head & Neck Cases

Faculty: Abberly Lott Limbach, MD, The Ohio State University Wexner Medical Center

Professional Practice Gap:

Head and neck tumors present a unique challenge to pathologists. Not only is the anatomy of the head and neck complex, but the area includes tissue types like those found elsewhere the body as well as tissue types only found in the head and neck. This complexity means that the pathologist often faces an ever-expanding differential diagnosis. Adding to the confusion, tumors from other sites can metastasize to the head and neck. Given the rarity of head and neck specimens combined with the broad differential diagnosis pathologists can be uncomfortable with assessing and diagnosing these tumors. This session will present a series of unusual head and neck tumors as well as more common tumors presenting unusually in the head and neck, drawn from day-to-day practice at a tertiary-care hospital that draws patients from across the region. The cases will be used a framework for the diagnosis of complex head and neck tumors.

Learning Objectives:

  1. Integrate knowledge of head and neck anatomy and clinical information to facilitate the work up of head and neck tumors
  2. Describe a differential diagnosis for unusual tumors in the head and neck
  3. Select and perform appropriate immunohistochemical stains to differentiate between head and neck tumors

Hematopathology: The Common and the Uncommon

Faculty: Sandeep Gurbuxani, PhD, MBBS, University of Chicago

Professional Practice Gap:

Hematopathology has been at the cutting edge of translating new discoveries into clinical workflow to fine tune disease diagnosis and sub-classification. With increasing use of massively parallel sequencing (more commonly referred to as next generation sequencing or NGS), it has become clear that on the one hand, morphologically identical neoplasms may show molecular heterogeneity and on the other, some morphologically dissimilar entities may converge on common molecular pathways. This is reflected in the recently published International Consensus Classification and the 5th Edition of WHO classification with an expanded number of entities that are defined by genetics. The impact of genetics is additionally visible in diagnosis of AML where the 20% blast threshold is no longer need in the presence of leukemia defining genetic lesions. Some of these uncommon genetic lesions present with common and non-specific clinical findings and pathology. On the other side, hematologic malignancies with commonly recognized mutations can have uncommon presentation. The session will used bone marrow and tissue biopsies from representative cases to provide a practical approach to correlating morphology with genetics to correctly diagnose and sub-classify hematologic malignancies according to the ICC and WHO-5 classifications.

Learning Objectives:

  1. Understand how morphology and immunophenotype maybe predictive of unusual genetics
  2. Recognize uncommon presentation of hematologic malignancies associated with common genetic lesions
  3. Understand the significance of correlating morphology with genomic studies to arrive at clinically actionable diagnoses that reflect the revised WHO and ICC classifications

Kidney/Renal Pathology

Renal Pathology for the Surgical Pathologist: What to See on the H&E, and Beyond

Faculty: Nidia Messias, MD, Barnes-Jewish Hospital/Washington University

Professional Practice Gap:

Renal pathology is not a Board-certified subspecialty, which may lead to the conclusion that surgical pathologists are proficient in diagnosing and interpreting medical renal pathology specimens (native and transplant). However, only 64% of pathology residency programs offer renal pathology as a mandatory elective (Paik,J, 2023).  Evaluation of kidney tissue on autopsies and nephrectomy specimens leaves much to be desired (Perrone ME, 2013; Sekar P, 2019).  Furthermore, the possibility of transplant rejection, evaluation of donor biopsies, and the diagnosis of RPGN are often listed as critical/urgent results (Soleimani, N 2023). These potentially urgent diagnosis may require in situ evaluation by a surgical pathologist that should be familiar with these entities, which does not occur due to lack of previous training/expertise in renal pathology.

Learning Objectives:

  1. Identify common pathology in renal specimens in non-neoplastic kidney tissue in nephrectomies, and autopsy cases
  2. Identify urgent/critical results in evaluation of renal pathology specimens, using H&E slides:
    • Identification of vasculitis and RPGN
    • Identification of transplant rejection
    • Identification of core findings in renal transplant donor biopsies
  3. Discuss pitfalls and limitations of the H&E results when compared with full evaluation by renal pathologists
  4. Explain what and when to defer diagnosis on kidney pathology specimens

Liver Pathology

The Protean Manifestations of Drug and Herbal Induced Liver Injury (DILI and HILI)

Faculty: Catriona McKenzie, MBBS, Royal Prince Alfred Hospital

Professional Practice Gap:

Medical liver biopsies have been historically performed to grade and stage biopsies and to establish diagnosis. The advent of fibroscan has reduced the number of protocol biopsies meaning that pathologists need to become increasingly familiar with biopsies performed for acute liver failure and deranged liver function tests which are typically performed to confirm or establish aetiology or to narrow differential diagnoses.  Drug and herbal induced liver injury (DILI and HILI) are important to consider in the differential diagnoses of many liver diseases as they have a wide range of histological appearances. As cessation of a drug, particularly in cancer patients, can have serious implications for ongoing management it is important that pathologists both recognize the wide patterns of injury that can be seen and have a structured framework for establishing causality for DILI or HILI.

Learning Objectives:

  1. Identify and describe the broad range of histopathological injury patterns seen in DILI including checkpoint inhibitors, other prescription drugs, herbal supplements and toxins
  2. Use a pattern-based approach to describe the injury pattern seen to narrow differential diagnoses
  3. Develop a structured causality assessment framework to attribute liver injury to DILI
  4. Learn practical approaches for assessment of medical liver biopsies


Frozen Sections from the Liver: Not as Hard as Ice

Faculty: Vishal Chandan, MD, University of California, Irvine

Professional Practice Gap:

Recently there has been an increasing adaptation of “sub-specialty” sign-out within surgical pathology. However, most “sub-specialized” surgical pathologists still provide “general” coverage of intra-operative consultation service (frozen section coverage from every organ/system). Frozen section diagnosis can sometimes be challenging when handling them alone during the call hours or on the weekends, especially if they are outside your practicing “sub-specialty.” Frozen section interpretation is primarily based on histologic features seen on the slide at that moment, as it is not possible to use adjuvant tests like immunohistochemical stains and molecular tests. The pathologist is often also under pressure as time is of the essence.

Despite the advances in imaging techniques, intra-operative frozen sections from the liver still play an important role in the immediate management of patients undergoing abdominal surgeries. Most frozen sections performed on the liver are for assessing hepatic metastases (in patients undergoing potentially curative resections for a primary malignancy of the pancreas, stomach and esophagus) or margin evaluation for partial hepatic resections. Frozen sections are also used to determine the suitability of potential donor livers.

This course will discuss the most common clinical scenarios and indications for frozen sections from the liver. It will also highlight the common mimickers and critical artifacts to avoid misinterpretations. The attendees will improve their competency, efficiency, and confidence when communicating with their surgeons and overall turn-around time. This course will also stress the importance of evaluating the fresh gross specimen on resection cases and also knowing if the background liver is cirrhotic or not.  We will also discuss when deferral of a frozen section diagnosis is a valid option to avoid ambiguous interpretation and potential for harmful error. Finally, this course will highlight the criteria for evaluating liver donor biopsies using frozen sections.

Learning Objectives:

  1. Explain the common indications and clinical scenarios for which frozen sections from the liver may be requested.
  2. Identify characteristic morphologic features to distinguish metastatic adenocarcinoma from benign glandular lesions/proliferations.
  3. Distinguish primary hepatic neoplasms from their mimickers on frozen sections.
  4. Generate a meaningful frozen section diagnosis and communicate effectively with the surgeon.
  5. Discuss the assessment of donor liver biopsy for organ transplant evaluation.


Add These to Your Differential Diagnoses of Liver Tumors: Entities that You May Not Be Thinking of While Working up a Liver Lesion

Faculty: Maria Westerhoff, MD, University of Michigan

Professional Practice Gap:

The goal of this interactive microscopy course is for pathologists to build their differential diagnoses regarding liver lesions and gain more confidence in working them up:

  1. Cholangiocarcinoma (3 cases: intrahepatic, extrahepatic, and intraductal papillary neoplasm of the bile duct): There is a difference in the embryologic origins of intrahepatic and extrahepatic cholangiocarcinomas. Pathologists may not know that albumin ISH will be useful in intrahepatic but may not be in extrahepatic cholangiocarcinomas. Some of the lesions such as intrahepatic intraductal papillary neoplasm of the bile duct have terminology that is intimidating and new to pathologists.
  2. Vascular tumors of the liver (3 cases: Hepatic small vessel neoplasm, angiosarcoma, epithelioid hemangioendothelioma): Some extremely subtle vascular neoplasms such as hepatic small vessel neoplasm can cause architectural changes to the liver parenchyma; these may then end up mimicking hepatocellular neoplasms such as hepatocellular adenomas or hepatocellular carcinoma so closely, leading to misdiagnosis. Pathologists may not know that hepatic small vessel neoplasms can be distinguished from hepatic tumors and other vascular tumors, such as angiosarcoma, by the use of careful histologic exam and molecular methods. Epithelioid hemangioendotheliomas can be very sneaky on biopsy because they may be focally present in the sinusoids or mimic carcinomas because of keratin positivity and ability to cause atypical epithelioid morphology. Immunostains can be very helpful, but pathologists have to be able to put this entity on their differential diagnosis of carcinoma-like tumors in the first place.
  3. Hepatoid non-hepatic tumors in the liver (3 cases: metastatic neuroendocrine tumors with pink cytoplasm, metastatic acinar cell carcinoma, angiomyolipoma). Metastatic tumors are the most common cause of liver masses. Pathologists may be unaware that tumors with eosinophilic cytoplasm that are hepatoid in appearance can be positive for liver markers. Acinar cell carcinoma can be positive for albumin-ISH and glypican 3. Neuroendocrine tumors with pink cytoplasm can also be positive for HCC markers. Finally, angiomyolipomas can morphologically mimic HCC, even containing areas of steatosis. Pathologists may misdiagnose these tumors based on lack of careful morphologic examination and an immunohistochemical panel that is too narrow.

Learning Objectives:

  1. Be aware of the differences between intrahepatic and extrahepatic cholangiocarcinomas that may affect their pathology and staining characteristics, as impacts diagnostic workup.
  2. Describe the diagnostic features and workup of various hepatic vascular neoplasms.
  3. Avoid misdiagnosis of hepatoid non-liver tumors by identifying key histologic features and spurious staining characteristics that may potentially cause an erroneous diagnosis of hepatocellular neoplasia.

A Journey into the Ailments of the Brain: Postmortem Examination

Faculty: Mireille Bitar, MD, Children’s Hospital Los Angeles

Professional Practice Gap:

Autopsy is an essential part of pathology residency training, as it provides a valuable educational experience in human disease processes, clinical–pathologic correlation, and anatomy. Performing autopsies during pathology training is required for the anatomic pathology board eligibility. Today, less than 10% of all hospital deaths are followed by an autopsy (PMID: 17467518). Furthermore, autopsies can be limited and exclude the central nervous system examination. A report by the Association of Pathology Chairs on assessing autopsy competency in pathology residency training acknowledged the decline in autopsy rate and recommend that autopsy should remain an essential part of pathology training and education (PMID: 30783620).

Learning Objectives:

  1. Identify and describe various vascular, infectious, neoplastic, and demyelinating disorders of the central nervous system through gross images and histologic examination of brain autopsies
  2. Perform a focused differential diagnosis and identify ancillary tests that would assist in the diagnosis
  3. Enhance confidence in reporting brain autopsies


Pancreas, Gallbladder, Ampulla, and Extra-Hepatic Biliary Tree

Small Biopsies of the Pancreatobiliary System: Tips and Tricks for the Practicing Pathologist

Faculty: Aatur Singhi, MD, PhD, University of Pittsburgh Medical Center

Professional Practice Gap:

In recent years, small biopsies of the pancreas (e.g., fine-needle biopsies) and bile duct (e.g., forceps biopsies) have gained widespread popularity among gastroenterologists. However, the associated specimens are also among the most challenging to evaluate, even for the subspecialized gastrointestinal pathologist. The difficulties associated with diagnostic interpretation are largely attributed to their limited tissue yields, fragmented nature, obscured by hemorrhage and gastrointestinal tract contaminants, and, in certain scenarios, susceptibility to tissue artifacts (e.g., crushing artifacts). As a result, multiple potential diagnostic pitfalls exist and, hence, a solid foundation in the key clinicopathologic and immunohistochemical characteristics of pancreatobiliary lesions is essential.

Within this interactive microscopy session, attendees will be asked to evaluate and discuss a series of small biopsy specimens to formulate an appropriate differential diagnosis based on the clinical and imaging findings given, along with providing a limited immunohistochemical panel of stains to arrive at the correct diagnosis. Within this session, the attendees will review the clinicopathologic findings of these lesions and, in parallel be exposed to novel stains (e.g., DAXX, ATRX, YAP1, and others) to aid in the distinction between these entities. Similarly, other entities that enter the differential of solid and cystic lesions will be covered to end with a discussion regarding associated molecular alterations that are helpful clues.

There are several professional practice gaps with regard to these pancreatobiliary specimens. For example, the distinction between pancreatic neuroendocrine tumors (PanNETs) and pancreatic neuroendocrine carcinomas (PanNECs). PanNETs and PanNECs have clear differences in clinical presentation, outcome and, more importantly, therapeutic approach (PMID: 26482044 and 27759713). Hence, accurate classification of pancreatic neuroendocrine neoplasms is critical for appropriate patient management. Frequent modifications in nomenclature and prognostic grading systems of pancreatic neuroendocrine neoplasms within the past two decades has created confusion as to the appropriate use of terminology. Further, among high-grade (G3) pancreatic neuroendocrine neoplasms, distinguishing PanNET and a PanNEC can be challenging (PMID: 25723112). In fact, in a study among pathologists with extensive experience in neuroendocrine neoplasms, a consensus diagnosis could not be reached in two-thirds of G3 pancreatic neuroendocrine neoplasms on the basis of morphology alone.

Similar practice gaps include the diagnosis of pancreatic ductal adenocarcinoma versus chronic pancreatitis (e.g., autoimmune pancreatitis, type 1), especially on small biopsies. In addition, the distinction between cellular neoplasms, such as solid-pseudopapillary neoplasms, acinar cell carcinomas, pancreatoblastomas, and well-differentiated neuroendocrine tumors can be challenging without a clear understanding of what stains to order. These issues are compounded when considering the classification and prognostication of pancreatic cysts including the interpretation of Moray forceps biopsies and pancreatic cyst fluid molecular testing. Further, bile duct biopsies are often associated with poor sensitivity, which is not solely due to sampling limitations but rather pathologic interpretation, appropriate use of immunohistochemical stains, and, once again, understanding of the relevance of specific genomic alterations found in bile duct biopsy specimens.

Learning Objectives:

  1. Discuss the histologic differences between pancreatic ductal adenocarcinoma and chronic pancreatitis (e.g., autoimmune pancreatitis, type 1) using small biopsy specimens
  2. Distinguish between reactive biliary epithelium and invasive adenocarcinoma using ERCP-obtained bile duct biopsies based on histomorphologic findings and ancillary immunohistochemistry
  3. Explain the clinical, radiographic, serologic, histologic, and immunophenotypic differences between non-ductal solid pancreatic neoplasms using small biopsy specimens


Pulmonary Pathology

A Practical Approach to Lymphoid Neoplasms of the Lung and Pleura

Faculty: Katalin Kelemen, MD, PhD, Mayo Clinic

Professional Practice Gap:

Most pathologists evaluate a large number of lung biopsies with carcinoma and are familiar with the diagnosis and ancillary testing in this context. However, lymphoid proliferations in lung and pleura represent a challenge. The diagnosis of lymphoma has a profound impact on the clinical management. Pathologist should be equipped with a practical diagnostic approach and should understand how to use ancillary tests efficiently. Our experience in a high-volume pulmonary pathology consultation practice shows that lung biopsies with lymphoid proliferations are often submitted for expert consultation and represent a diagnostic challenge for many pathologists. Furthermore, pathologists struggle with the selection of appropriate ancillary tests, sometimes exhausting limited samples before a diagnosis can be reached.

Learning Objectives:

  1. Describe a diagnostic approach to the biopsy of a lung mass showing a lymphoid infiltrate composed of small lymphocytes and plasma cells, using immunohistochemistry and an appropriate B-lymphoid clonality testing for the diagnosis of pulmonary MALT lymphoma, and to differentiate from other types of low-grade B-cell lymphomas.
  2. Describe a diagnostic approach to mass lesions that may be associated with MALT lymphoma in the lung, including amyloidosis, light chain deposition disease, and crystal storing histiocytosis 3, 4, 5.
  3. Describe a diagnostic approach to the diagnosis of diffuse large B-cell lymphoma in the lung, with or without a concomitant pulmonary MALT lymphoma 6.
  4. Describe a diagnostic approach to classic Hodgkin lymphoma in the lung.
  5. Understand the clinical spectrum of EBV-positive large B-cell lymphomas that occur in the lung and describe a diagnostic approach to these types of lymphomas. Acquire knowledge of the new terminology assigned by WHO-5 and ICC classifications 1, 2.
  6. Describe a diagnostic approach to large cell lymphomas occurring in pleural fluid and know how to differentiate between HHV8+ and HHV8- primary effusion lymphomas versus other types of large cell lymphomas in this context 1, 2.