Cholangiocarcinoma with respect to IgG4 Reaction

Role of IgG4 Antibodies in Human Health and Disease

Immunoglobulin G4 (IgG4), a unique subclass of IgG antibodies, plays diverse roles in human health and disease. Its distinct features, such as Fab-arm exchange and specific mutations, confer reduced effector functions compared to other IgG subclasses. In health, IgG4 responses contribute to immune tolerance, particularly in the context of allergen-specific immunotherapy (AIT), where they can mediate tolerance to environmental antigens, inhibit IgE-dependent mast cell degranulation, and compete with IgE for allergen binding. This helps in attenuating allergic symptoms and is associated with increased levels of allergen-specific IgG4. However, in disease scenarios, the role of IgG4 is complex. IgG4 lacks complement fixation and, thus, shows a reduced ability to activate immune effector pathways, it was initially thought to be protective against autoimmune diseases. However, emerging evidence suggests that it can contribute to pathology. For instance, IgG4 autoantibodies against specific antigens can aggravate conditions in certain autoimmune disorders. In some cancers, it may play a role in immune evasion, with higher levels correlating with poor patient survival, albeit in others, its exact function remains elusive. Overall, understanding the precise role of IgG4 in various physiological and pathological conditions is crucial for developing targeted therapeutic strategies and improving patient outcomes.

Uncommon Benign Neoplasms and Pseudotumors of the Liver

CONTEXT.—

The most common benign hepatic mass-forming lesions often display fairly specific imaging characteristics, whereas less familiar, rarer benign neoplasms and pseudotumors may pose a diagnostic challenge in clinical, radiology, and pathology practice because of either their rarity or their unusual features.

OBJECTIVE.—

To review a selection of pseudotumors and unusual benign hepatic neoplasms encountered in consultation practices with a focus on nonepithelial tumors.

DATA SOURCES.—

Sources include English-language literature and personal experiences.

CONCLUSIONS.—

Several benign conditions (namely, segmental atrophy, infections, immunoglobulin G4 [IgG4]-related sclerosing disease, angiomyolipoma, mesenchymal hamartoma, and various vascular lesions) can lead to formation of hepatic masses. Because of their rarity and underrecognition, such lesions are often diagnostically challenging. Awareness of hepatic pseudotumors and various rare hepatic neoplasms and their potential mimics can forestall misdiagnosis and inappropriate management.

Association Between Immunoglobulin G4-Related Ophthalmic Disease and Nonlymphoid Malignancy Case Series and Comprehensive Review of the Literature

BACKGROUND

Immunoglobulin G4-related disease (IgG4-RD) and immunoglobulin G4-related ophthalmic disease (IgG4-ROD) complicated with nonlymphoid malignancy (NL-malignancy) are rare. No exact relationship between IgG4-RD and NL-malignancies has been established yet, and there have been few reports of different types of IgG4-ROD and related malignancies.

METHODS

We retrospectively reviewed medical records of patients diagnosed with IgG4-RD and NL-malignancy, whichever occurred first, from January 2015 to March 2021. In addition, the literature on the relationship between IgG4-ROD and NL-malignancy was reviewed.

RESULTS

There were 115 patients diagnosed with IgG4-RD, and 10 patients were enrolled in the study with NL-malignancy. Three patients were diagnosed with IgG4-ROD. One patient reported a previous history of cancer, and the other 2 patients developed cancer at or after the diagnosis of IgG4-RD. The 3 patients' cancers were located in the lung, gastrointestinal tract, and thyroid.

CONCLUSIONS

There may be potential malignancy occurrence during follow-up of IgG4-RD patients, especially among elderly patients. In addition, IgG4-RD could be a paraneoplastic syndrome at or before the diagnosis of malignancy.

IgG4-related autoimmune liver disease

The term IgG4-related autoimmune liver disease (AILD) refers to hepato-biliary manifestations of Immunoglobin G4-related disease (IgG4-RD) including IgG4-related sclerosing cholangitis and IgG4-related pseudotumor. The association of some forms of autoimmune hepatitis to IgG4-RD remains controversial. Although autoimmune phenomena have not been clearly observed in IgG4-AILD, perturbation of the adaptive immune system and activation of the humoral response represent established pathophysiological hallmarks and potential therapeutic targets. Clinical manifestations of IgG4-AILD are virtually indistinguishable from bile duct cancer or primary sclerosing cholangitis and are due to mass forming lesions and thickening of the biliary tract that progressively lead to biliary ducts obstruction. There are no current reliable biomarkers for IgG4-AILD and diagnosis should rely on the integration of clinical, serological, radiological, and histological findings. In analogy to most IgG4-RD manifestations, and in contrast to its major mimickers, IgG4-AILD promptly responds to glucocorticoids but frequently relapses, thus requiring long-term maintenance therapy to avoid progressive fibrosclerotic disease and liver cirrhosis. Accumulating evidence on the efficacy of B-cell depletion therapy in patients with systemic IgG4-RD is gradually changing the treatment paradigm of IgG4-AILD and biologics will be increasingly used also for gastroenterological manifestations of IgG4-RD to spare glucocorticoids and traditional immunosuppressive agents. Looking ahead, identification of reliable biomarkers and of mini-invasive strategies to obtain informative biopsies from the biliary tree represent unavoidable priorities to optimize diagnosis and management of IgG4-AILD.

Tumor-B-cell interactions promote isotype switching to an immunosuppressive IgG4 antibody response through upregulation of IL-10 in triple negative breast cancers

BACKGROUND

Triple negative breast cancer (TNBC) is an aggressive breast cancer for which there is currently no targeted therapy. Tumor-infiltrating B-cells (TIB) have been observed in tumor tissues of TNBC patients, but their functional role is unclear. IgG4 is one of four antibody subclasses of IgG expressed and secreted by B cells. Unlike other IgG isotypes, IgG4 has an immunosuppressive function and is induced by Th2-type cytokines. In cancers such as melanoma, IgG4 has been linked with advanced disease and poor patient survival. Therefore, we sought to determine if IgG4 + B cells are present and determine the mechanisms driving isotype switching in TNBC.

METHODS

We performed co-culture assays to examine expression of Th2 cytokines by TNBC cells with and without the presence of B cells. We also performed in vitro class switching experiments with peripheral B cells with and without co-culture with TNBC cells in the presence or absence of an IL-10 blocking antibody. We examined expression of CD20+ TIB, IgG4 and Th2 cytokines by immunohistochemistry in 152 TNBC samples. Statistical analysis was done using Log-Rank and Cox-proportional hazards tests.

RESULTS

Our findings indicate that B cells interact with TNBC to drive chronic inflammatory responses through increased expression of inflammatory cytokines including the TH2 cytokines IL-4 and IL-10. In vitro class switching studies show that interactions between TNBC cell lines and B cells drive isotype switching to the IgG4 isotype in an IL-10 dependent manner. In patient tissues, expression of IgG4 correlates with CD20 and tumor expression of IL-10. Both IgG4 and tumor IL-10 are associated to shorter recurrence free survival (RFS) and overall survival (OS) in TNBC. In a multi-variant analysis, IL-10 was associated with poor outcomes indicating that tumor IL-10 may drive immune escape.

CONCLUSIONS

These findings indicate that interactions between TIB and TNBC results in activation of chronic inflammatory signals such as IL-10 and IL-4 that drive class switching to an IgG4 + subtype which may suppress antibody driven immune responses. The presence of IgG4 + B cells may serve as a biomarker for poor prognosis.

Autoimmune Pancreatitis with Gastric Cancer: Some IgG4-related Diseases May Be Paraneoplastic Syndrome

A 70-year-old man was referred to our department for the treatment of early gastric cancer. Contrast-enhanced computed tomography (CT) incidentally showed diffuse enlargement of the pancreas with a capsule-like rim, and blood tests showed elevated serum IgG4 levels, leading to a diagnosis of autoimmune pancreatitis (AIP). Endoscopic treatment for gastric cancer was performed, and pathological findings showed adenocarcinoma with abundant IgG4-positive plasma cell infiltration. Thereafter, the serum IgG4 levels normalized, and the findings of AIP disappeared on CT without steroid treatment. These findings suggest that the gastric cancer activated an IgG4-related immune response, resulting in the development of AIP.

Intracranial Tumors Associated With IgG4-Related Disease

IgG4-related disease (IgG4-RD) is an immune-mediated inflammatory condition which is characterized by dense lymphoplasmacytic infiltrations with a predominance of IgG4 plasma cells in the affected tissue. Although pachymeninx and pituitary gland are the most common sites where IgG4-RD infiltrates, the associations with IgG4-RD and a true intracranial tumor have not been yet reported in literature. Herein, we report two cases with intracranial tumors associated with IgG4-RD; a 36-year-old male patient with a huge meningioma and another 54-year old woman with a pituitary macroadenoma. Pathological examination revealed their tumors were substantially infiltrated by IgG4 plasma cells indicating its possible relation with IgG4-RD.

Significance of high serum IgG4 in complete or non-full-fledged IgG4-related disease-a retrospective investigation of 845 patients and its clinical relevance

OBJECTIVE

Immunoglobulin G4-related disease (IgG4-RD) is a recently recognized heterogeneous, subacute, and usually silent autoimmune disease involving many organs with protean manifestations. However, high IgG4 in serum is not necessarily indicating an IgG4-RD. The aims of this study were to investigate the clinical relevance of high serum IgG4 level in IgG4-RD or non IgG4-RD patients, and to see if IgG4-RD in Taiwan differs from that in other parts of the world.

METHODS

Eight hundred forty-five patients with high IgG4 were retrospectively reviewed from January 2002 to May 2020 in Taipei Veteran General Hospital. Two hundred sixty-seven patients fulfilled IgG4-RD criteria and were categorized into pancreato-hepato-biliary disease, retroperitoneal fibrosis and/or aortitis, head/neck-limited disease, classic Mikulicz syndrome with systemic involvement, CNS-limited disease, sclerosing vasculitis, skin-limited disease, and sensorineural hearing disease. These manifestations were correlated to smoking, atopy, hyper-IgE/eosinophilia, aging, malignancies, and hypocomplementemia. Five hundred seventy-eight patients were not fulfilling the criteria but were also analyzed for the prevalence of allergy, malignancy, connective tissue diseases, lung diseases, and infections.

RESULTS

In IgG4-RD patients, 124 (46.4%) smoked. Top 4 clinical subtypes included Mikulicz syndrome with systemic involvement (33.3%), pancreato-hepatobiliary disease (31.4%), head/neck disease (19.4%), and retroperitoneal fibrosis/aortitis (12.7%). Top 4 co-morbid conditions included high serum IgE/eosinophilia (46.2%), hypocomplementemia (34%), malignancies (13.4%), and allergy (13.4%). Pancreato-biliary disease was associated with high IgE/eosinophilia (r² = 0.380, P = 0.025) and malignancy (r² = 0.211, P = 0.027), Miculicz syndrome with allergy (r² = 0.396, P < 0.01) and high IgE/eosinophil (r² = 0.396, P < 0.01), CNS diseases (r² = 0.973, P = 0.035) and sclerosing vasculitis (r² = 1, P < 0.01) with advanced age respectively, with the latter being also related to atopy and high IgE/eosinophilia (r² = 1, p < 0.01).

CONCLUSION

Smoking may precipitate IgG4-RD. IgG4-RD with pancreato-hepatobiliary disease is closely related to allergy and neoplasm, and those with Mikulicz syndrome may result from atopy. Elderly IgG4-RD patients tend to develop CNS pathology parallel to advancing of age. The disease may probably be originated from an unknown mechanism that may sporadically evolve into malignancies.

IgG4-related Sclerosing Cholangitis Complicated with Cholangiocarcinoma and Detected by Forkhead Box P3 Immunohistochemical Staining

An 80-year-old man was admitted due to biliary stricture with autoimmune pancreatitis. Although radiographical examinations suggested Immunoglobulin G4-related sclerosing cholangitis (IgG4-SC), punched biopsies from the bile duct revealed adenocarcinoma. In the resected specimen, abundant N-terminus of Forkhead box P3 (Foxp3)-positive cells were localized in cholangiocarcinoma (CCA) tissue, while IgG4-positive cells were spread around the entire bile duct. Therefore, the case was diagnosed with IgG4-SC accompanied by CCA, not sporadic CCA. We herein report an informative case wherein IgG4-positive cells were abundant in CCA tissue and Foxp3 immunohistochemical staining allowed us to determine that this case had two entities.

The neglected brothers come of age: B cells and cancer

The opposing roles of innate and adaptive immune cells in suppressing or supporting cancer initiation, progression, metastasis and response to therapy has been long debated. The mechanisms by which different monocyte and T cell subtypes affect and modulate cancer have been extensively studied. However, the role of B cells and their subtypes have remained elusive, perhaps partially due to their heterogeneity and range of actions. B cells can produce a variety of cytokines and present tumor-derived antigens to T cells in combination with co-stimulatory or inhibitory ligands based on their phenotype. Unlike most T cells, B cells can be activated by innate immune stimuli, such as endotoxin. Furthermore, the isotype and specificity of the antibodies produced by plasma cells regulate distinct immune responses, including opsonization, antibody-mediated cellular cytotoxicity (ADCC) and complement activation. B cells are shaped by the tumor environment (TME), with the capability to regulate the TME in return. In this review, we will describe the mechanisms of B cell action, including cytokine production, antigen presentation, ADCC, opsonization, complement activation and how they affect tumor development and response to immunotherapy. We will also discuss how B cell fate within the TME is affected by tumor stroma, microbiome and metabolism.

Klatskin tumor diagnosed concurrently with IgG4 related sclerosing cholangitis: A case report

RATIONALE

IgG4-related disease (IgG4-RD) is a systemic disease that can involve various organs and is characterized by the infiltrations of IgG4-positive plasma cells and lymphocytes, fibrosis, and elevated serum IgG4 levels. IgG4-related sclerosing cholangitis (IgG4-RSC) is a subtype of IgG4-RD. No certain relationship between IgG4-RSC and cholangiocarcinoma has been established as yet, and there have been few reports of the simultaneous diagnosis of IgG4-RSC and cholangiocarcinoma.

PATIENT CONCERNS

A 76-year-old male visited our gastroenterology department due to the recent occurrence of pruritus and jaundice.

DIAGNOSIS

Computed tomography (CT) scan showed ductal wall swelling and enhancement from both intrahepatic duct confluence to the common bile duct, upper biliary dilatation, and accompanying autoimmune pancreatitis (a sub type of IgG4-RD). Biopsy of the distal common bile duct by endoscopic retrograde cholangiopancreatography (ERCP) resulted in a diagnosis of IgG4-RSC. Subsequently, adenocarcinoma was identified by repeated cytology of bile juice. Finally, Klatskin tumor type IIIA and IgG4-RSC were concurrently diagnosed.

INTERVENTIONS

IgG4-RSC was treated with steroid and Klatskin tumors by gemcitabine + cisplatin chemotherapy.

OUTCOMES

The jaundice had improved and CT showed substantial improvement of the intrahepatic duct dilatation.

LESSONS

IgG4-RSC and cholangiocarcinoma are easily confused, but their treatments are quite different, and thus, care must be taken during diagnosis. Furthermore, these 2 diseases may co-exist. Therefore, even if IgG4-RSC is diagnosed first, the possibility of accompanying cholangiocarcinoma should be thoroughly investigated.

The Role of IgG4 in the Fine Tuning of Tolerance in IgE-Mediated Allergy and Cancer

Among the four immunoglobulin G (IgG) subclasses, IgG4 is the least represented in serum of a healthy human and it is considered an “odd” antibody. The IgG4 antibody has unique structural features that affect its biological function. These include the ability to undergo antigen-binding fragment (Fab)-arm exchange, to create fragment crystallizable (Fc) – Fc binding with other IgG4 and other IgG subclass antibodies, have a unique affinity profile for Fc gamma receptors (FcγRs) and no binding to complement component C1q. Altogether, these characteristics support anti-inflammatory roles of IgG4 leading to immune tolerance. Under conditions of chronic antigenic stimulation and Th2-type inflammation, both tissue and serum IgG4 levels are increased. This review seeks to highlight how in allergen immunotherapy IgG4 can confer a protective role as a “blocking” antibody and safeguard from subsequent allergen exposure, while IgG4 can confer immunomodulatory functions to support malignancy. While Th2 conditions drive polarization of macrophages to the M2a subtype, chronic antigen stimulation drives B cell class switching to IgG4 to further support phenotypical macrophage changes towards an M2b-like state. M2b-like macrophages can secrete chemokine (C-C motif) ligand 1 (CCL1) and interleukin-10 (IL-10) to support regulatory cell recruitment and to further shape a tolerogenic microenvironment. Thereby, IgG4 have a Janus-faced role, favorable in allergy but detrimental in cancer.

IgG4-type Multiple Myeloma with Diffuse Enlargement of the Thyroid Requiring Differentiation from IgG4-related Disease

We herein report a 65-year-old man with elevated serum IgG4 levels, enlarged thyroid, and renal dysfunction, mimicking IgG4-related disease (IgG4-RD). The definitive diagnosis of IgG4-RD was not established because a tissue biopsy revealed no IgG4-positive cell infiltration or fibrosis. The presence of an M peak in the β fraction, Bence Jones protein in urine, and progressive anemia suggested multiple myeloma (MM). The κ/λ ratio was >100, tumor plasma cells were present at >20% in bone marrow, and immunostaining revealed IgG4-positive plasma cells; therefore, he was diagnosed with IgG4-type MM. Patients with elevated IgG4 levels with no significant mass lesions should undergo systemic examinations to exclude malignancy.

Clinical practice guidelines for IgG4-related sclerosing cholangitis

IgG4‐related sclerosing cholangitis (IgG4‐SC) is a distinct type of cholangitis frequently associated with autoimmune pancreatitis and currently recognized as a biliary manifestation of IgG4‐related disease. Although clinical diagnostic criteria of IgG4‐SC were established in 2012, differential diagnosis from primary sclerosing cholangitis and cholangiocarcinoma is sometimes difficult. Furthermore, no practical guidelines for IgG4‐SC are available. Because the evidence level of most articles retrieved through searching the PubMed, Cochrane Library, and Igaku Chuo Zasshi databases was below C based on the systematic review evaluation system of clinical practice guidelines MINDS 2014, we developed consensus guidelines using the modified Delphi approach. Three committees (a guideline creating committee, an expert panelist committee for rating statements according to the modified Delphi method, and an evaluating committee) were organized. Eighteen clinical questions (CQs) with clinical statements were developed regarding diagnosis (14 CQs) and treatment (4 CQs). Recommendation levels for clinical statements were set using the modified Delphi approach. The guidelines explain methods for accurate diagnosis, and safe and appropriate treatment of IgG4‐SC.

An Imposter Twice Over: A Case of IgG4-Related Disease

IgG4-RD has the ability to mimic other pathologic conditions, requiring that health care professionals have a high index of suspicion to make a proper diagnosis.

Desmoplastic Tumor Microenvironment and Immunotherapy in Cholangiocarcinoma

Cholangiocarcinoma (CCA) is a dismal disease which often is diagnosed at a late stage where the tumor is locally advanced, metastatic, and, as a result, is associated with low resectability. The heterogeneity of this cancer type is a major reason why the majority of patients fail to respond to therapy, and surgery remains their only curative option. Among patients who undergo surgical intervention, such tumors typically recur in 50% of cases within 1year. Thus, CCA is among the most aggressive and chemoresistant malignancies. CCA is characterized by marked tumor reactive stroma, a fibrogenic connective tissue which surrounds and infiltrates the tumor epithelium. This desmoplastic environment presents a clinical challenge, limiting drug delivery and supporting the growth of the tumor mass. In this review we attempt to highlight key pathways involved in cell to cell communication between the tumor epithelium and stroma, the immune components, and opportunities for novel strategies to improve patient outcome.

Clinical Implications of Cytotoxic T Lymphocyte Antigen-4 Expression on Tumor Cells and Tumor-Infiltrating Lymphocytes in Extrahepatic Bile Duct Cancer Patients Undergoing Surgery Plus Adjuvant Chemoradiotherapy

BACKGROUND

There currently is only limited knowledge on the role of tumor-specific immunity in cholangiocarcinoma.

OBJECTIVE

This study evaluated the clinical implications of cytotoxic T lymphocyte antigen-4 (CTLA-4) expression levels and CD4+ and CD8+ tumor-infiltrating lymphocytes (TILs) in extrahepatic bile duct (EHBD) cancer.

PATIENTS AND METHODS

Immunohistochemistry of CTLA-4, CD4, and CD8 was performed for 77 EHBD cancer patients undergoing surgery plus adjuvant chemoradiotherapy. CTLA-4 expression on tumor cells and TILs were assessed by using H-scores and the proportion of CTLA-4+ lymphocytes, respectively.

RESULTS

With optimal cutoff values determined by a maximal chi-square method with overall survival (OS) data, patients with CTLA-4 H-score >70 and a proportion of CTLA-4+ TILs >0.15 showed higher mean density of CD8+ and CD4+ TILs, respectively (P = 0.025 for CD8+ and P = 0.055 for CD4+ TILs). The high CTLA-4 H-score level was associated with prolonged OS and disease-free interval (DFI) (P = 0.025 and 0.004, respectively). With differential levels of CTLA-4 H-score according to hilar and non-hilar locations (high rate 32 vs. 68%, respectively; P = 0.013), an exploratory subgroup analysis demonstrated that the associations between the CTLA-4 expression and OS and DFI were confined to hilar tumors (P = 0.003 and <0.001, respectively), but not to non-hilar ones (P = 0.613 and 0.888, respectively).

CONCLUSIONS

This study demonstrates a potential prognostic relevance of CTLA-4 expression in EHBD cancer. We suggest a differential survival impact of the CTLA-4 expression level according to different tumor locations.

Increased Immunoglobulin G4-positive Plasma Cells in Lymphadenoma of the Salivary Gland: An Immunohistochemical Comparison Among Lymphoepithelial Lesions

BACKGROUND

Lymphadenoma (LA) of the salivary gland, nonsebaceous type, is an uncommon benign lymphoepithelial neoplasm. The histogenesis of the lymphoid component of LA is under debate as in Warthin's tumor. A recent study has described immunoglobulin (Ig) class switching to IgG4 in a subset of Warthin's tumors. The aim of this study is to evaluate IgG4 status of LA and presume the role of IgG4 status in pathogenesis of LA.

MATERIALS AND METHODS

The distribution of IgG-positive and IgG4-positive cells was compared by immunohistochemistry among 15 lymphoepithelial lesions of the salivary gland (8 LAs, 3 lymphoepithelial carcinomas, and 4 lymphoepithelial cysts). Epstein-Barr virus in situ hybridization was also performed.

RESULTS

IgG-positive and IgG4-positive plasma cells were observed in all cases, but to a remarkable degree (IgG4>100/hpf) in 2 of 8 LAs. The IgG4 plasma cells in LA were distributed in interfollicular areas and in the vicinity of epithelial nests. Among all cases, the mean number of IgG4 plasma cells was not correlated with the presence of germinal centers (12/15) or Epstein-Barr virus positivity (2/15).

CONCLUSIONS

Increased IgG4 plasma cells in LA suggest involvement of an immune reaction in the pathogenesis of LA similar to Warthin's tumor.

Immunoglobulin G4-mediated sclerosing cholangitis as a risk factor for cholangiocarcinoma: A case report

Immunoglobulin (Ig)G4-mediated disease is a systemic autoimmune disease, which occasionally presents solely as sclerosing cholangitis (SC). IgG4-mediated SC is challenging to diagnose, as it may mimic cholangiocarcinoma radiologically, and carcinoma cells may produce IgG4. The diagnosis of IgG4-mediated disease is based on histological consensus criteria and response to corticosteroids. In addition to the radiological and histological overlap between IgG4-mediated SC and cholangiocarcinoma, IgG4-mediated SC may be considered as a risk factor for the development of cholangiocarcinoma. We herein present the case of a patient in whom cholangiocarcinoma developed in two lesions previously characterized as IgG4-mediated SC, including a suggested mechanism underlying the contribution of IgG4-mediated SC to the development of cholangiocarcinoma.

Ocular adnexal marginal zone lymphoma arising in a patient with IgG4-related ophthalmic disease

A 41-year-old man was diagnosed with immunoglobulin G4-related disease (IgG4-RD) in both eyelids 4 years ago and exhibited good response to steroid therapy. However, rapid swelling of the right eyelid lesion was recently observed. As IgG4-RD progression was suspected, biopsy was performed. Although the histology was consistent with IgG4-RD, the infiltrating large atypical lymphoid cells showed immunoglobulin light-chain restriction and IgH gene rearrangement. Consequently, he was diagnosed with extranodal marginal zone lymphoma with abundant IgG4-positive cells.

Adult bile duct strictures: differentiating benign biliary stenosis from cholangiocarcinoma

Biliary epithelial cells preferentially respond to various insults under chronic pathological conditions leading to reactively atypical changes, hyperplasia, or the development of biliary neoplasms (such as biliary intraepithelial neoplasia, intraductal papillary neoplasm of the bile duct, and cholangiocarcinoma). Moreover, benign biliary strictures can be caused by a variety of disorders (such as IgG4-related sclerosing cholangitis, eosinophilic cholangitis, and follicular cholangitis) and often mimic malignancies, despite their benign nature. In addition, primary sclerosing cholangitis is a well-characterized precursor lesion of cholangiocarcinoma and many other chronic inflammatory disorders increase the risk of malignancies. Because of these factors and the changes in biliary epithelial cells, biliary strictures frequently pose a diagnostic challenge. Although the ability to differentiate neoplastic from non-neoplastic biliary strictures has markedly progressed with the advance in radiological modalities, brush cytology and bile duct biopsy examination remains effective. However, no single modality is adequate to diagnose benign biliary strictures because of the low sensitivity. Therefore, understanding the underlying causes by compiling the entire clinical, laboratory, and imaging data; considering the under-recognized causes; and collaborating between experts in various fields including cytopathologists with multiple approaches is necessary to achieve an accurate diagnosis.

IgG4 Characteristics and Functions in Cancer Immunity

IgG4 is the least abundant subclass of IgG in normal human serum, but elevated IgG4 levels are triggered in response to a chronic antigenic stimulus and inflammation. Since the immune system is exposed to tumor-associated antigens over a relatively long period of time, and tumors notoriously promote inflammation, it is unsurprising that IgG4 has been implicated in certain tumor types. Despite differing from other IgG subclasses by only a few amino acids, IgG4 possesses unique structural characteristics that may be responsible for its poor effector function potency and immunomodulatory properties. We describe the unique attributes of IgG4 that may be responsible for these regulatory functions, particularly in the cancer context. We discuss the inflammatory conditions in tumors that support IgG4, the emerging and proposed mechanisms by which IgG4 may contribute to tumor-associated escape from immune surveillance and implications for cancer immunotherapy.