Immunoglobulin light chain immunohistochemistry revisited, with emphasis on reactive follicular hyperplasia versus follicular lymphoma

Isolated Light Chain-restricted Germinal Centers are Common in Follicular Hyperplasia by Ultrasensitive In Situ Hybridization

Ultrasensitive bright-field RNA in situ hybridization (BRISH) can be used to detect lower levels of light chain expression than immunohistochemical stains or conventional colorimetric RNA in situ hybridization. In this study, we retrospectively reviewed 77 lymph node specimens with follicular hyperplasia and kappa/lambda BRISH performed as part of the diagnostic evaluation. Thirty-two of the specimens had ≥1 germinal center(s) (GC) showing light chain restriction (14 specimens with lambda-restricted GC, 9 with kappa-restricted GC, and 9 with separate kappa-restricted or lambda-restricted GC). In all but 1 specimen, the light chain-restricted GC represented a minority of the total GC (average: 10%, range: 0.2% to 60%). There was no significant difference in age, sex, type of biopsy (core vs. excision), number of GCs, proportion of cases with a light chain-restricted B-cell population by flow cytometry, or proportion of cases with a positive IgH gene rearrangement study between the specimens with and without restricted GCs. In our cohort of follicular hyperplasia cases, BRISH identified light chain-restricted GC more frequently than flow cytometry identified a monotypic B-cell population. Our findings highlight the potential for overinterpretation of light chain restriction in limited samplings such as fine needle aspiration cell blocks or core needle sampling and reinforce that interpretation of BRISH staining needs to occur in the context of the morphologic features including tissue architecture and results of additional immunohistochemical stains.

Use of Ultrasensitive RNA In Situ Hybridization for Determining Clonality in Cutaneous B-Cell Lymphomas and Lymphoid Hyperplasia Decreases Subsequent Use of Molecular Testing and Is Cost-effective

Primary cutaneous B-cell lymphomas (PCBCLs) are diagnostically challenging entities due to significant overlap in clinical and morphologic features with reactive lymphoid proliferations. Traditional methods for evaluating clonality such as immunohistochemistry (IHC) and chromogenic in situ hybridization (CISH) are limited by low sensitivity, which leads to additional costly and time-consuming molecular clonality assays. More recent technology has introduced ultrasensitive bright-field RNA in situ hybridization (BRISH) to the field, which can detect single molecules of light-chain mRNA. The current study evaluated 274 cases of PCBCL in addition to atypical and reactive lymphoid infiltrates, with CISH or BRISH performed on 180 (65.7%). CISH was performed on 105 (58.3%), and BRISH was performed on 75 (41.7%). Significantly fewer immunoglobulin heavy-chain (IGH) rearrangement studies were performed on cases that were evaluated with BRISH as compared with CISH (P=0.02). Subgroup analysis demonstrated that cases with restriction by BRISH were significantly less likely to have subsequent IGH studies performed (P=0.01). The expected costs of cases using CISH versus BRISH were $1053.89 versus $810.32 to the patient and $245.63 versus $225.23 to the laboratory. The use of ultrasensitive BRISH to evaluate clonality in PCBCL reduced the use of IGH rearrangement studies when compared with CISH. In particular, cases with light-chain restriction by BRISH did not result in confirmatory molecular testing. Despite slightly higher costs to the laboratory to perform BRISH, routine use of this methodology can result in cost savings to both the patient and laboratory by decreasing the use of expensive molecular methods.

Morphological and immunohistochemical approaches to the diagnosis of Hashimoto thyroiditis and mucosa associated lymphoid tissue lymphomas: An audit

Most cases of autoimmune hypothyroidism are due to Hashimoto thyroiditis (HT). It is sometimes difficult to distinguish HT from mucosa associated lymphoid tissue (MALT) lymphoma using cytology or histology alone. This has necessitated the use of immunohistochemistry and other molecular techniques. A descriptive study was undertaken to determine the prevalence of MALT lymphoma and other associations of HT using histopathological and immunohistochemical methods. For testing of kappa and lambda antibodies, paraffin sections were prepared for immunohistochemical staining using a peroxidase-antiperoxidase immune complex method. Immunostaining in HT, demonstrated a polyclonal lymphoid population, as evidenced by dual positivity for kappa and lambda staining cells, whereas MALT lymphoma revealed a monoclonal lymphoid population, with strong positivity for kappa immunostaining and lack of lambda light chain expression. The proportion of MALT lymphoma in surgically treated cases of HT in the present study was 3.5% (95% CI: 0%–8.3%). The common malignancy associated with HT was papillary carcinoma of the thyroid (8.8%). Among the benign conditions, nodular colloid goiter (7%) was more commonly associated. Although modern molecular techniques are available for the confirmation of lymphomas, they are more expensive, time consuming and are available only in a few centers. Strict morphological criteria can differentiate HT from MALT lymphoma, but in suspicious cases, paraffin section immunohistochemistry using light chain restriction can offer comparable and reliable results. Since papillary carcinoma and MALT lymphoma have been associated with HT, these patients require careful surveillance.

Kappa and lambda immunohistochemistry and in situ hybridization in the evaluation of atypical cutaneous lymphoid infiltrates

BACKGROUND

Atypical cutaneous lymphoid infiltrates are challenging lesions in dermatopathology. We present a summary of the literature regarding kappa and lambda immunohistochemistry (IHC) and in situ hybridization (ISH) in the evaluation of atypical cutaneous or mucosal lymphoid infiltrates.

METHODS

Relevant articles from 1967 to 2018 in the English language were identified and summarized. In the absence of larger studies, case series of n ≥ 3 were included.

RESULTS

Sixty-three articles assessing kappa and lambda IHC and/or ISH were identified. Most focused on marginal zone lymphomas. Other lymphomas included follicle center lymphoma, diffuse large B-cell lymphoma, chronic lymphocytic leukemia/small lymphocytic lymphoma, mantle cell lymphoma, lymphoplasmacytic lymphoma, plasmablastic lymphoma, multiple myeloma, monoclonal gammopathy of undetermined significance, and polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, skin changes (POEMS). Non-neoplastic lesions included reactive lymphoid hyperplasia, cutaneous plasmacytosis, connective tissue disease, IgG4-related disease, acrodermatitis chronic atrophicans, Zoon balanitis, dermatitides, and infiltrates around epithelial dysplasias/neoplasias.

CONCLUSION

Kappa and lambda IHC and ISH are useful tools in the evaluation of cutaneous B-cell lymphomas and plasma cell neoplasms. The literature supports that the detection of light-chain restriction by IHC and ISH is one of the most useful findings in the differential diagnosis of reactive lymphoid hyperplasia vs B-cell lymphoma with plasmacytic differentiation.

Chromogenic in situ hybridization for the detection of lambda and kappa immunoglobulin light chains as a potential auxiliary diagnostic technique in canine plasmacytomas

The heterogeneous morphologic features of canine plasmacytomas (PCTs) can make their differentiation from other round cell tumors challenging. Immunohistochemistry (IHC) for lambda (λ) and kappa (к) immunoglobulin (Ig) light chains is often equivocal because of high background staining. The chromogenic in situ hybridization (CISH) technique for light chains has shown higher sensitivity compared to IHC in human plasma cell tumors. Therefore, we aimed to validate automated CISH for light chains in canine tissues and to evaluate its diagnostic potential in canine PCTs, in conjunction with routinely used IHC markers. CISH for light chains demonstrated a clear signal in plasma cell populations of canine control tissues (lymph nodes, lymphoplasmacytic inflammation) showing a polyclonal pattern with a prevalence of λ-producing cells. CISH detected monotypic light chain expression in 33 of 53 (62%) PCTs, 31 expressing λ and 2 expressing к. CISH was more sensitive than IHC for λ light chain (58% vs. 47%, respectively) and more easily interpretable given the absence of confounding background staining. The absence of CISH staining for both λ and к in a considerable subset of tumors may be the result of lower light chain production by neoplastic cells. Multiple myeloma oncogene 1 (MUM1) was expressed by all but 2 PCTs (96%), which showed λ expression by CISH and IHC. The identification of poorly differentiated canine PCTs requires the assessment of a panel of IHC markers, with the potential support of CISH for Ig light chains.

Ultrasensitive automated RNA in situ hybridization for kappa and lambda light chain mRNA detects B-cell clonality in tissue biopsies with performance comparable or superior to flow cytometry

The assessment of B-cell clonality is a critical component of the evaluation of suspected lymphoproliferative disorders, but analysis from formalin-fixed, paraffin-embedded tissues can be challenging if fresh tissue is not available for flow cytometry. Immunohistochemical and conventional bright field in situ hybridization stains for kappa and lambda are effective for evaluation of plasma cells but are often insufficiently sensitive to detect the much lower abundance of light chains present in B-cells. We describe an ultrasensitive RNA in situ hybridization assay that has been adapted for use on an automated immunohistochemistry platform and compare results with flow cytometry in 203 consecutive tissues and 104 consecutive bone marrows. Overall, in 203 tissue biopsies, RNA in situ hybridization identified light chain-restricted B-cells in 85 (42%) vs 58 (29%) by flow cytometry. Within 83 B-cell non-Hodgkin lymphomas, RNA in situ hybridization identified restricted B-cells in 74 (89%) vs 56 (67%) by flow cytometry. B-cell clonality could be evaluated in only 23/104 (22%) bone marrow cases owing to poor RNA preservation, but evaluable cases showed 91% concordance with flow cytometry. RNA in situ hybridization allowed for recognition of biclonal/composite lymphomas not identified by flow cytometry and highlighted unexpected findings, such as coexpression of kappa and lambda RNA in 2 cases and the presence of lambda light chain RNA in a T lymphoblastic lymphoma. Automated RNA in situ hybridization showed excellent interobserver reproducibility for manual evaluation (average K=0.92), and an automated image analysis system showed high concordance (97%) with manual evaluation. Automated RNA in situ hybridization staining, which can be adopted on commonly utilized immunohistochemistry instruments, allows for the interpretation of clonality in the context of the morphological features in formalin-fixed, paraffin-embedded tissues with a clinical sensitivity similar or superior to flow cytometry.

Rare case report of an aggressive follicular lymphoid hyperplasia in maxilla

Follicular lymphoid hyperplasia is a very rare though benign reactive process of an unknown pathogenesis that may resemble a follicular lymphoma, clinically and histologically. Oral reactive follicular hyperplasia (RFH) has been described on the hard or soft palate and at the base of the tongue. We describe here the first case of RFH presenting as an aggressive tumor on the right posterior side of the maxilla in a 24-year-old male patient. The lesion had a clinical evolution of 18 months and was noticed after the surgical extraction of the right third molar, although we cannot assume a cause-effect relation with that surgical event whatsoever. His medical history was unremarkable. Following an incisional biopsy, histological examination revealed lymphoid follicles comprised by germinal centers surrounded by well-defined mantle zones. The germinal centers were positive for Bcl-6, CD10, CD20, CD21, CD23, CD79a, and Ki-67, while negative for Bcl-2, CD2, CD3, CD5, and CD138. The mantle and interfollicular zones were positive for Bcl-2, CD2, CD3, CD5, CD20, and CD138. Both areas were diffusively positive for kappa and lambda, showing polyclonality. The patient underwent a vigorous curettage of the lesion with no reoccurrences at 36 months of follow-up. This case report demonstrates that morphologic and immunohistochemical analyses are crucial to differentiate RFH from follicular lymphoma, leading to proper management.

Multimodality Technologies in the Assessment of Hematolymphoid Neoplasms

Accurate assessment of tissues for hematolymphoid neoplasms requires an integrated multiparameter approach. Although morphologic examination by light microscopy remains the mainstay of initial assessment for hematolymphoid neoplasms, immunophenotypic analysis by immunohistochemistry and/or flow cytometry is essential to determine the pattern of differentiation and to detect minimal disease when morphology is inconclusive. In some cases, immunophenotypic analysis provides additional information for targeted immunotherapy and prognostication. Genotypic studies, including cytogenetics, fluorescence in situ hybridization, DNA microarray, polymerase chain reaction, and/or next-generation sequencing, are also imperative for subclassification of the genetically defined disease entities in the current World Health Organization classification of hematolymphoid neoplasms. Moreover, genotypic studies can establish clonality, stratify patients to determine appropriate treatment, and monitor patients for treatment response.

The B Cell-Stimulatory Cytokines BLyS and APRIL Are Elevated in Human Periodontitis and Are Required for B Cell-Dependent Bone Loss in Experimental Murine Periodontitis

B-lineage cells (B lymphocytes and plasma cells) predominate in the inflammatory infiltrate of human chronic periodontitis. However, their role in disease pathogenesis and the factors responsible for their persistence in chronic lesions are poorly understood. In this regard, two cytokines of the TNF ligand superfamily, a proliferation-inducing ligand (APRIL) and B-lymphocyte stimulator (BLyS), are important for the survival, proliferation, and maturation of B cells. Thus, we hypothesized that APRIL and/or BLyS are upregulated in periodontitis and contribute to induction of periodontal bone loss. This hypothesis was addressed in both human and mouse experimental systems. We show that, relative to healthy controls, the expression of APRIL and BLyS mRNA and protein was upregulated in natural and experimental periodontitis in humans and mice, respectively. The elevated expression of these cytokines correlated with increased numbers of B cells/plasma cells in both species. Moreover, APRIL and BLyS partially colocalized with κ L chain-expressing B-lineage cells at the epithelial-connective tissue interface. Ligature-induced periodontitis resulted in significantly less bone loss in B cell-deficient mice compared with wild-type controls. Ab-mediated neutralization of APRIL or BLyS diminished the number of B cells in the gingival tissue and inhibited bone loss in wild-type, but not in B cell-deficient, mice. In conclusion, B cells and specific cytokines involved in their growth and differentiation contribute to periodontal bone loss. Moreover, APRIL and BLyS have been identified as potential therapeutic targets in periodontitis.

Benign lymphadenopathies

Benign lymphadenopathy is a common biopsy finding, and may often be confused with malignant lymphoma. It may be separated into major morphologic patterns, each with its own differential diagnosis with certain types of lymphoma. Most cases of reactive follicular hyperplasia is easy to diagnosis, but some cases may be confused with follicular lymphoma, but key morphologic, immunohistochemical, and molecular findings may usually distinguish between the two, particularly assessment of bcl-2 staining. Molecular studies to demonstrate B-cell clonality, as well as the t(14;18), may also be of great use in difficult cases. IgG4-associated sclerosing disease is discussed, as one recently described example of a specific type of reactive follicular hyperplasia in which the etiology may be suggested based on pathologic studies. While overlapping with the other types of hyperplasia, a high index of suspicion as well as IgG and IgG4 immunostains will help raise the possibility of the diagnosis that can be confirmed by further clinical studies. Reactive paracortical/interfollicular hyperplasia is another pattern of reactive hyperplasia, which may easily be confused with Hodgkin and non-Hodgkin lymphoma, particularly T-cell lymphoma. Epstein-Barr virus-associated infectious mononucleosis is an example of reactive paracortical/interfollicular hyperplasia, which may often simulate a malignant lymphoma. Attention to clinical findings, as well as a combination of immunohistochemical stains and in situ hybridization studies for Epstein-Barr early RNA (EBER) will usually allow a definitive diagnosis. In addition, lymph nodes with extensive necrosis may simulate malignant lymphoma. Kikuchi necrotizing histiocytic lymphadenitis is an example of a benign process with extensive necrosis, which may easily be confused with non-Hodgkin lymphoma. Clinical and morphologic features, particularly the presence of abundant karyorrhectic debris along with a paucity of granulocytes, as well as immunohistochemical studies to rule out lymphoma, are most helpful in establishing the correct diagnosis.