Increased CD5-positive polyclonal B cells in Castleman disease: a diagnostic pitfall

Unmet Clinical Needs in the Management of Idiopathic Multicentric Castleman Disease: A Consensus-based Position Paper From an ad hoc Expert Panel

Castleman disease describes a group of heterogeneous clinicopathological disorders now included in the tumor-like lesions with B-cell predominance of the World Health Organization classification. Managing idiopathic multicentric Castleman disease (iMCD) is challenging, because few systematic studies or comparative randomized clinical trials have been conducted. International, consensus evidence-based guidelines for iMCD were published in 2018, but gaps in the therapeutic options for difficult-to-treat patients, who do not respond to siltuximab and other conventional therapies, still exist. This article presents the results of group discussion among an ad hoc constituted Panel of Italian experts to identify and address unmet clinical needs (UCNs) in managing iMCD. Recommendations on the appropriateness of clinical decisions and proposals for new research concerning the identified UCNs were issued through formalized multiple-step procedures after a comprehensive analysis of the scientific literature. The following key UCNs were addressed: strengthening the diagnostic certainty in iMCD patients before planning first-line therapy; management of siltuximab therapy; choice and management of immune-modulating, or chemotherapy agents in patients resistant/intolerant to siltuximab therapy. While most of the conclusions reached by the Panel are consistent with the existing guidelines, some alternative therapeutic options were stressed, and the discussion contributed to bringing forth the issues that need further investigation. Hopefully, this comprehensive overview will improve the practice of iMCD and inform the design and implementation of new studies in the field.

[Castleman disease]

The term "Castleman disease" covers a variety of entities that have very different clinical, biological, pathological and physiopathological features. In this issue, we review the characteristics of the unicentric Castleman disease, of the HHV8 associated multicentric Castleman disease and the idiopathic multicentric Castleman disease associated or not with TAFRO syndrome ("thrombocytopenia, anasarca, fever, reticulin myelofibrosis and/or renal insufficiency, organomegaly"). We detail the differential diagnostics of these entities.

La maladie de Castleman : aspects anatomopathologiques

Histologically, Castleman's disease associates three subtypes: 1-the vascular hyaline (HV) subtype more often seen in unicentric forms; 2-the plasmacytic (PV) subtype, more frequently associated with the HHV8+ and idiopathic multicentric form; 3-the mixed subtype associating both HV and PV aspects that may be encountered in any type of Castleman's disease. If the diagnosis of unicentric (isolated mass) and multicentric HHV8+ Castleman's disease is easy, the diagnosis of the idiopathic multicentric form remains particularly difficult because it is at the crossroads of many other pathologies (infectious, tumoral and dysimmune), making an anatomoclinical comparison necessary. The role of the pathologist, in the context of disseminated lesions (polyadenopathy and splenomegaly), is to identify lesions that may be part of Castleman's disease, to systematically perform HHV8 testing and to perform complete phenotyping associated with molecular analysis (B and T-cell clonality) in order to rule out a lymphomatous process and certain infectious etilogies. In all cases, its role will be a warning bell and the diagnosis of Castleman's disease will be retained only after a rigorous anatomic and clinical confrontation. © 2022 Published by Elsevier Masson SAS on behalf of Société nationale française de médecine interne (SNFMI).

IgG4-related disease and idiopathic multicentric Castleman's disease: confusable immune-mediated disorders

IgG4-related disease (IgG4-RD) and idiopathic multicentric Castleman's disease (iMCD) are both rare systemic immune-mediated disorders. However, pathogenesis differs markedly between the two diseases, and differing therapeutic strategies are adopted: IgG4-RD is treated using a moderate dose of glucocorticoids or rituximab, while iMCD therapy involves an interleukin (IL)-6 targeted approach. Nonetheless, some clinical features of IgG4-RD and iMCD overlap, so differential diagnosis is sometimes difficult, even though the classification and diagnostic criteria of the diseases require careful exclusion of the other. The key findings in IgG4-RD are high IgG4/IgG ratio, allergic features, and germinal centre expansion involving T follicular helper cells, while iMCD involves polyclonal antibody production (high IgA and IgM levels), sheet-like mature plasma cell proliferation, and inflammatory features driven by IL-6. The distribution of organ involvement also provides important clues in both diseases. Particular attention should be given to differential diagnosis using combined clinical and/or pathological findings, because single features cannot distinguish IgG4-RD from iMCD. In the present review, we discuss the similarities and differences between IgG4-RD and iMCD, as well as how to distinguish the two diseases.

Mantle Cell Lymphoma With Mantle Zone Growth Pattern

OBJECTIVES

To characterize the clinical and pathologic features of mantle cell lymphoma with mantle zone growth pattern (MCL-MZGP).

METHODS

The clinicopathologic data from 35 cases of MCL-MZGP obtained in 12 centers were analyzed.

RESULTS

The patients with MCL-MZGP typically sought treatment at high clinical stages (81%). Intriguingly, 40% (14/35) of cases were incidentally noted. The lymph nodes with MCL-MZGP showed preserved architecture and expanded mantles containing lymphoma cells with classic or small cell cytology. MCL-MZGP was positive for BCL2 (96%, bright), CD5 (82%, moderate), cyclin D1 (100%), and SOX11 (89%). Clinically, our study revealed no significant difference in the overall survival between patients managed with observation alone and those who received chemotherapy.

CONCLUSIONS

MCL-MZGP was often incidentally identified and resembled reactive mantles. Therefore, recognition of this unusual morphology emphasizes the utility of cyclin D1 immunostain in the cases with suspicious morphology. However, the clinical significance of these findings is still unclear.

Castleman Disease

Castleman disease (CD) is divided clinically into unicentric or multicentric type. Pathologically, CD is divided into hyaline-vascular and plasma cell variants. Unicentric CD is most common, about 75% of these cases are hyaline-vascular variant, and surgical excision is often curative. In contrast, there are a number of types of multicentric CD including HHV8-associated, idiopathic, and a subset of cases that arise in association with POEMS syndrome. Therapy is required for most patients with multicentric CD, but there is no consensus approach currently. As is evidence, the designation Castleman disease encompasses a heterogeneous group of diseases of varied pathogenesis and which require different therapies.

Pathology of Castleman Disease

The term Castleman disease encompasses several distinct lymphoproliferative disorders with different underlying disease pathogenesis, and clinical outcomes. It includes unicentric and multicentric diseases with limited versus significant systemic symptoms, respectively. Importantly, the histopathologic features encountered in the various forms of Castleman disease are diverse, and for the most part, lack specificity, because they are seen to varying degrees in different clinical variants of Castleman disease, and in reactive (autoimmune/infectious) and malignant (lymphoma) contexts. Accordingly, accurate clinical diagnosis of Castleman disease requires careful and thorough clinicopathologic correlation. An overview of the key histopathologic features of Castleman disease is presented.