How I treat: diagnosing and managing "in situ" lymphoma

B Lymphoproliferative Neoplasms of Uncertain Biological Significance: Report from the IV Workshop of the Italian Group of Hematopathology and Review of the Literature

Lymphoproliferative neoplasms of uncertain biological significance are increasingly encountered due to widespread usage of immunophenotypic and molecular techniques. Considering that clearer biological criteria and patient management have been established for B-cell lymphoproliferative diseases of undetermined significance occurring in the peripheral blood, many issues are still obscure for early lesions detected in lymphoid tissues. Regardless that some categories of lymphoproliferative neoplasms of uncertain biological significance have been recognized by the 4th edition of the WHO, other anecdotal early lymphoproliferative lesions still remain fully undefined. Some early lesions frequently originate from the germinal center, including atypical germinal centers BCL2-negative, an early pattern of large B-cell lymphoma with IRF4 rearrangement, and “in situ” high-grade B lymphomas. Moreover, other early lymphoproliferative lesions arise outside the germinal center and include those developing within the setting of monocytoid B-cell hyperplasia, but they also can be directly or indirectly associated with chronic inflammations. This review aims to summarize the concepts discussed during the IV Workshop organized by the Italian Group of Hematopathology, focus on the state-of-the-art on B-cell lymphoproliferative neoplasms of uncertain biological significance, and offer operative insights to pathologists and clinicians in routine diagnostics.

Is Limited-Stage Mantle Cell Lymphoma Curable and How Is It Best Managed?

Limited-stage (stage I-II) mantle cell lymphoma (MCL) is rarely encountered. There is no standard approach to treatment and available data to guide management decisions mainly are retrospective studies. A thorough staging evaluation, including positron emission tomography/computed tomography, bone marrow biopsy, and gastrointestinal evaluation, should be completed because disseminated disease is common. Radiation therapy is effective for local control, and, although prolonged remission can be achieved, distant relapses are common and there are insufficient data to say that patients can be cured using this treatment. This article reviews literature pertaining to management of patients with limited-stage MCL and discusses approach to treatment.

Prevalence of Lymphoid Neoplasia in a Retrospective Analysis of Warthin Tumor: A Single Institution Experience

Warthin tumor is one of the most common benign salivary gland tumors. Overt lymphoma is known to occur in the lymphoid stroma of Warthin tumor. In situ follicular neoplasia is difficult to identify in routine histologic examination of lymphoid tissue and has not been reported in association with Warthin tumor. Our objective is to determine the prevalence of overt malignant lymphoma and in situ follicular neoplasia in Warthin tumor. We conducted a retrospective histological evaluation of 89 sequential Warthin tumor cases with available slides and blocks from the years 2010-2019. Of these, 84 cases were subjected to immunohistochemical testing, while 5 cases had been previously worked up for the suspicion of lymphoma. We identified two additional cases of lymphoid neoplasia associated with Warthin tumor including small lymphocytic lymphoma/chronic lymphocytic leukemia (n = 1) and in situ follicular neoplasia (n = 1) in addition to previously reported case of follicular lymphoma included in this study. The prevalence rate of first-time detected lymphoid neoplasia in Warthin tumor is 3.4%. The prevalence rate of overt lymphoma is 2.2%, while the prevalence of in situ follicular neoplasia is 1.1%. We propose histologic criteria to identify small lymphocytic lymphoma and follicular lymphoma in Warthin tumor. These include a monotonous interfollicular expansion of small lymphocytes and germinal centers composed of a monotonous population of lymphocytes without polarity or tingible body macrophages respectively. It is very important for pathologists to perform a diligent morphological examination and perform immunohistochemistry in suspected cases to identify subtle involvement of Warthin tumor by lymphoma. In patients with involvement of Warthin tumor by in situ follicular neoplasia, concurrent lymphoma in the same tissue and other sites should be considered. Patients without overt lymphoma elsewhere likely have a low risk of progression to follicular lymphoma. The low prevalence of in situ follicular neoplasia in Warthin tumor, combined with the low rate of clinical progression to lymphoma, make routine screening of Warthin tumor for in situ follicular neoplasia unnecessary.

The broad landscape of follicular lymphoma: Part I

Follicular lymphoma is a neoplasm derived from follicle center B cells, typically both centrocytes and centroblasts, in variable proportions according to the lymphoma grading. The pattern of growth may be entirely follicular, follicular and diffuse, and rarely completely diffuse. It represents the second most common non-Hodgkin lymphoma, after diffuse large B-cell lymphoma and is the most common low-grade mature B-cell lymphoma in western countries. In the majority of cases, follicular lymphoma is a nodal tumor, occurring in adults and frequently associated with the translocation t(14;18)(q32;q21)/IGH-BCL2. However, in recent years the spectrum of follicular lymphoma has expanded and small subsets of follicular lymphoma, which differ from common follicular lymphoma, have been identified and included in the current 2017 WHO classification. The aim of our review is to describe the broad spectrum of follicular lymphoma, pointing out that the identification of distinct clinicopathological variants of follicular lymphoma is relevant for patient outcomes and choice of treatment.

Follicular lymphoma

Follicular lymphoma (FL) is a systemic neoplasm of the lymphoid tissue displaying germinal centre (GC) B cell differentiation. FL represents ~5% of all haematological neoplasms and ~20-25% of all new non-Hodgkin lymphoma diagnoses in western countries. Tumorigenesis starts in precursor B cells and becomes full-blown tumour when the cells reach the GC maturation step. FL is preceded by an asymptomatic preclinical phase in which premalignant B cells carrying a t(14;18) chromosomal translocation accumulate additional genetic alterations, although not all of these cells progress to the tumour phase. FL is an indolent lymphoma with largely favourable outcomes, although a fraction of patients is at risk of disease progression and adverse outcomes. Outcomes for FL in the rituximab era are encouraging, with ~80% of patients having an overall survival of >10 years. Patients with relapsed FL have a wide range of treatment options, including several chemoimmunotherapy regimens, phosphoinositide 3-kinase inhibitors, and lenalidomide plus rituximab. Promising new treatment approaches include epigenetic therapeutics and immune approaches such as chimeric antigen receptor T cell therapy. The identification of patients at high risk who require alternative therapies to the current standard of care is a growing need that will help direct clinical trial research. This Primer discusses the epidemiology of FL, its molecular and cellular pathogenesis and its diagnosis, classification and treatment.

Follicular lymphoma in situ in the spleen of a patient with autoimmune hemolytic anemia and carrying HCV was associated with more clonal B-cells than t(14;18) positive B-cells

Certain autoimmune conditions are associated with an increased risk of lymphoid malignancy. We report a 65-year old patient with autoimmune hemolytic anemia (AIHA) complicated by a follicular lymphoma (FL) in situ and other B-cell clones in the spleen. This diagnosis was made by immunohistochemistry, flow cytometry, and Southern blot analysis of the B-cell receptor. Chromosomal analysis revealed 46,XX,t(14;18)(q32;q21) 2/20, 46,XX,del(7)(q?),del(11)(q?) 2/20, and 46,XX 16/20. It has been speculated that these preneoplastic conditions do not progress to overt FL and other lymphomas without a second lymphomagenic insult. However, AIHA confers a 27.4-fold higher risk of such an insult leading to lymphoma compared with the normal healthy population. Without any therapy after splenectomy, our current study patient remained healthy with no lymphoma development for 28 months. Based on this case, we discuss the pathophysiology of lymphomagenesis in a spleen with AIHA and the roles of a splenectomy for preventing further lymphomagenesis in AIHA patients.

Isolated Follicles Enriched for Centroblasts and Lacking t(14;18)/BCL2 in Lymphoid Tissue: Diagnostic and Clinical Implications

We sought to address the significance of isolated follicles that exhibit atypical morphologic features that may be mistaken for lymphoma in a background of reactive lymphoid tissue. Seven cases that demonstrated centroblast-predominant isolated follicles and absent BCL2 staining in otherwise-normal lymph nodes were studied. Four of seven cases showed clonal B-cell proliferations amid a polyclonal B cell background; all cases lacked the IGH-BCL2 translocation and BCL2 protein expression. Although three patients had invasive breast carcinoma at other sites, none were associated with systemic lymphoma up to 44 months after diagnosis. The immunoarchitectural features of these highly unusual cases raise the question of whether a predominance of centroblasts and/or absence of BCL2 expression could represent a precursor lesion or atypical reactive phenomenon. Differentiating such cases from follicular lymphoma or another mimic is critical, lest patients with indolent proliferations be exposed to unnecessarily aggressive treatment.

Lymphocytosis, lymphadenopathy: benign or malignant?

The increasing use of immunophenotypic and molecular analysis in the routine evaluation of patients with lymphocytosis, lymphadenopathy, or other hematologic disorders has led to the identification of unexpected small clonal lymphoid populations. These clones, sometimes with disease-specific markers, such as the t(14;18), are especially challenging for the clinician because of their unknown biologic potential and uncertain clinical behavior. Study of these early lymphoid lesions is providing important clues to the process of lymphomagenesis, and may provide the rationale for preemptive therapy in the future. More and more, the hematologist/oncologist is consulted regarding otherwise healthy individuals with lymphadenopathy and/or lymphocytosis, and pathology reports that confound the referring internist or surgeon. The report does not name a malignant lymphoproliferative disorder, but is not completely “normal”. Does the patient have a benign or malignant condition? How should they be evaluated? Is treatment indicated? These patients prove challenging for the consulting hematologist as well as the referring physician. In this review, we will focus on some of these scenarios and attempt to provide guidance for their management.

Common progenitor cells in mature B-cell malignancies: implications for therapy

PURPOSE OF REVIEW

This review summarizes the recent progress in defining the patterns of genetic evolution giving rise to relapse in follicular lymphoma and multiple myeloma, and discusses their implications with respect to 'personalized medicine'.

RECENT FINDINGS

High-throughput sequencing studies have uncovered a large degree of clonal heterogeneity within tumors, and found that subclones have a variable contribution to relapse. Recent studies aimed at defining patterns of clonal evolution have revealed that serial tumors in some malignancies share their ancestry in a less evolved common progenitor cell (CPC) that bears only a subset of the mutations that are present in the fully evolved tumors that present clinically. This pattern of 'divergent evolution' means that the majority of 'actionable mutations' in tumor specimens are absent within the progenitors that give rise to relapse.

SUMMARY

Follicular lymphoma and multiple myeloma are clinically, biologically and genetically distinct mature B-cell malignancies. However, recent studies have found them to share important similarities in their patterns of genetic evolution. Tumor cells that constitute subclonal populations within these tumors, or between consecutive tumors, share their origins within a genetically less evolved common progenitor cell. This pattern of evolution indicates that current therapies are unable to eradicate these less evolved populations that are at the root of relapse. This suggests that in order to obtain the best results with modern 'targeted therapies' that are directed towards 'actionable mutations', these mutations should be considered within the context of the evolutionary stage at which mutations are acquired, not simply on a presence or absence basis.

Early lymphoid lesions: conceptual, diagnostic and clinical challenges

There are no "benign lymphomas", a fact due to the nature of lymphoid cells to circulate and home as part of their normal function. Thus, benign clonal expansions of lymphocytes are only rarely recognized when localized. Recent studies have identified a number of lymphoid proliferations that lie at the interface between benign and malignant. Some of these are clonal proliferations that carry many of the molecular hallmarks of their malignant counterparts, such as BCL2/IGH and CCND1/IGH translocations associated with the in situ forms of follicular lymphoma and mantle cell lymphoma, respectively. There are other clonal B-cell proliferations with low risk of progression; these include the pediatric variants of follicular lymphoma and marginal zone lymphoma. Historically, early or incipient forms of T/NK-cell neoplasia also have been identified, such as lymphomatoid papulosis and refractory celiac disease. More recently an indolent form of T-cell lymphoproliferative disease affecting the gastrointestinal tract has been described. Usually, CD8(+), the clonal cells are confined to the mucosa. The clinical course is chronic, but non-progressive. NK-cell enteropathy is a clinically similar condition, composed of cytologically atypical NK-cells that may involve the stomach, small bowel or colon. Breast implant-associated anaplastic large cell lymphoma is a cytologically alarming lesion that is self-limited if confined to the seroma cavity. Atypical lymphoid proliferations that lie at the border of benign and malignant can serve as instructive models of lymphomagenesis. It is also critical that they be correctly diagnosed to avoid unnecessary and potentially harmful therapy.

Multifocal mantle cell lymphoma in situ in the setting of a composite lymphoma

OBJECTIVES

Mantle cell lymphoma in situ (MCLIS) consists of immunophenotypically defined but histologically inapparent neoplastic cells restricted to narrow mantle zones, without expansion or invasion beyond the mantle zone. We report a unique case of MCLIS associated with a much more manifest nodal marginal zone lymphoma (MZL) in an inguinal lymph node, porta hepatis lymph node, and bone marrow.

METHODS

Biopsies from all three locations were evaluated using standard H&E-stained sections, immunohistochemistry, flow cytometry, metaphase cytogenetics, and/or fluorescence in situ hybridization (FISH).

RESULTS

This case is unique for three reasons. First, the histologically covert mantle cell lymphoma was multifocal, detected in all three locations using one or more of flow cytometry, immunohistochemistry, cytogenetics, and FISH. Second, the MCLIS was always accompanied by a more histologically dominant MZL. Third, where evaluable, it did not grow in an appreciable mantle zone distribution, presumably due to destruction of the normal nodal architecture by the neoplastic MZL cells and the resulting absence of recognizable follicles and mantle zones.

CONCLUSIONS

This unique case provides new insight into the pathogenesis of MCLIS.

A rare presentation of in situ mantle cell lymphoma and follicular lymphoma: a case report and review of the literature

A 65-year-old gentleman presented with left groin swelling over the course of two months. Physical exam revealed nontender left inguinal adenopathy, and computed tomography scans detected multiple lymph nodes in the mesenteric, aortocaval, and right common iliac regions. An excisional lymph node biopsy was performed. Pathologic evaluation demonstrated follicular center site which stained positive for PAX5, CD20, CD10, Bcl-2, Bcl-6, and mantle zone cells. These findings demonstrated CCND1 and CD5 positivity, suggesting composite lymphoma comprising follicular lymphoma (FL) with in situ mantle cell lymphoma (MCLIS). FL is known as indolent non-Hodgkin lymphoma; however, the clinical significance of a coexisting MCLIS continues to be elusive, and optimal management of these patients remains largely unknown. This case illustrates the diagnostic and therapeutic challenges of composite lymphomas. This paper also discusses advances in molecular pathogenesis and lymphoma genomics which offer novel insights into these rare diseases.

Follicular dendritic cell pattern in early lymphomas involving follicles

This article reviews the most typical follicular dendritic cell (FDC) patterns displayed by early lymphomas involving follicles. In in situ follicular lymphoma, FDCs form a well-developed round (spherical) dendritic meshwork with a sharp outline. Other patterns that can be seen include contracted/distorted/disintegrated FDC meshworks. In early mantle cell lymphoma with mantle zone pattern, FDCs compose an ill-outlined and loosely arranged "centrifugal" meshwork. In marginal zone lymphoma, the FDC meshwork forms a relatively well-developed nodular meshwork with irregular outlines. In nodular lymphocyte predominant (LP) Hodgkin lymphoma, LP tumor cells are localized within an environment with prominent FDC meshwork and rare or absent LP cells outside the nodules. In angioimmunoblastic T-cell lymphoma (AITL), scattered regressed germinal centers are usually noted, although hyperplastic germinal centers are seen during the early stages of the disease (EAITL). Identifying the FDC meshwork, mainly in association with blood vessels, constitutes one of the most typical findings of the disease. In conclusion, the morphologic pattern of the FDC meshwork in early lymphomas of follicular origin is heterogenous and differs according to the lymphoma subtypes. These FDC patterns are recognizable in the most typical cases when the lymphoma is in its early stage and still maintains a follicular/nodular pattern of growth. The FDC patterns seen in the CD21 and CD23 stains contribute to the recognition of early stages of lymphomas involving follicles. Conversely, tumor cell immunostains for BCL2, cyclin D1, and other stains form the basis for the definition of lymphoma subtypes.

Defective stromal remodeling and neutrophil extracellular traps in lymphoid tissues favor the transition from autoimmunity to lymphoma

Altered expression of matricellular proteins can become pathogenic in the presence of persistent perturbations in tissue homeostasis. Here, we show that autoimmunity associated with Fas mutation was exacerbated and transitioned to lymphomagenesis in the absence of SPARC (secreted protein acidic rich in cysteine). The absence of SPARC resulted in defective collagen assembly, with uneven compartmentalization of lymphoid and myeloid populations within secondary lymphoid organs (SLO), and faulty delivery of inhibitory signals from the extracellular matrix. These conditions promoted aberrant interactions between neutrophil extracellular traps and CD5(+) B cells, which underwent malignant transformation due to defective apoptosis under the pressure of neutrophil-derived trophic factors and NF-κB activation. Furthermore, this model of defective stromal remodeling during lymphomagenesis correlates with human lymphomas arising in a SPARC-defective environment, which is prototypical of CD5(+) B-cell chronic lymphocytic leukemia (CLL).

Follicular lymphoma in situ presenting as dermatopathic lymphadenopathy

Introduction. Follicular lymphoma in situ (FLIS) is a recently described entity with few cases recognized worldwide. To our knowledge, this is the first FLIS reported from West Africa. Case Presentation. We present the case of a 48-year-old civil servant with axillary lymphadenopathy discovered on routine mammography. On histology, a predominant reactive change with aggregates of melanophages was seen prompting a diagnosis of reactive lymphadenopathy. Immunohistochemistry done in our laboratory showed CD10 and Bcl-6 positive germinal centres with a small population of Bcl-2 positive germinal centre centre cells that were limited to some of the germinal centres. Conclusion. This highlights the use of immunohistochemistry in lymph node pathology—a resource which is very limited in our environment.

Follicular lymphoma-like B cells of uncertain significance (in situ follicular lymphoma) may infrequently progress, but precedes follicular lymphoma, is associated with other overt lymphomas and mimics follicular lymphoma in flow cytometric studies

In situ follicular lymphoma, more recently known as follicular lymphoma-like B cells of uncertain/undetermined significance is well accepted. However, the morphological criteria have evolved since it was first described and data are limited and conflicting regarding its clinical implications and whether the extent of involvement predicts an association with overt lymphoma. It is also unknown how often it will be identified by flow cytometric studies and how often it precedes overt follicular lymphomas. A multiparameter study of 31 biopsies with follicular lymphoma-like B cells of uncertain significance and 4 'benign' lymph node biopsies that preceded an overt follicular lymphoma was, therefore, performed. Fifty-two percent of biopsies with follicular lymphoma-like B cells were associated with a prior or concurrent lymphoma but only 6% subsequently developed lymphoma (median follow up 26 months). Neither the number, proportion or density of BCL2(+) germinal centers were associated with overt follicular lymphoma/diffuse large B-cell lymphoma. Flow cytometric studies identified follicular lymphoma-like B cells in 8 of 15 evaluable cases. The proportion but not the absolute number of BCL2(+) germinal centers was associated with the likelihood of positive flow cytometric studies (P<0.01). All 4 'benign' biopsies that preceded an overt follicular lymphoma demonstrated follicular lymphoma-like B cells. Thus, although few patients with follicular lymphoma-like B cells of uncertain significance progress within the follow-up period, it at least precedes many follicular lymphomas. The extent of involvement does not predict the occurrence of prior or concurrent lymphomas. Flow cytometric studies demonstrating follicular lymphoma-like B cells must not be over-interpreted as they may only reflect follicular lymphoma-like B cells.

MBL versus CLL: how important is the distinction?

Monoclonal B-cell lymphocytosis (MBL) is defined as a clonal B-cell expansion whereby the B-cell count is less than 5 × 10(9)/L and no symptoms or signs of lymphoproliferative disorders are detected. Based on B-cell count, MBL is further divided into low-count and clinical MBL. While low-count MBL seems to carry relevance mostly from an immunological perspective, clinical MBL and chronic lymphocytic leukemia appear to be overlapping entities. Only a deeper knowledge of molecular pathways and microenvironmental influences involved in disease evolution will help to solve the main clinical issue, i.e. how to differentiate nonprogressive and progressive cases requiring intensive follow-up.

Monoclonal B cell lymphocytosis and "in situ" lymphoma

The finding of monoclonal B-cell populations not fulfilling criteria for a lymphoid malignancy has given great impulse to study mechanisms involved in lymphomagenesis and factors responsible for the transition from B-cell precursor states to overt lymphoproliferative disorders. Monoclonal B cell expansions were initially recognized in peripheral blood of otherwise healthy subjects (thus defined monoclonal B-cell lymphocytosis, MBL) and in most cases share the immunophenotypic profile of chronic lymphocytic leukemia (CLL). The clinical relevance of this phenomenon is different according to B-cell count: high-count MBL is considered a preneoplastic condition and progresses to CLL requiring treatment at a rate of 1-2% per year, while low-count MBL, though persisting over time, has not shown a clinical correlation with frank leukemia so far. MBL other than CLL-like represent a minority of cases and are ill-defined entities for which clinical and biological information is still scanty. In situ follicular lymphoma (FL) and mantle cell lymphoma (MCL) are characterized by the localization of atypical lymphoid cells, carrying t(14;18)(q32;q21) or t(11;14)(q13;q32), only in the germinal centers and mantle zones respectively, where their normal counterparts are localized. The localization of these cells indicates that germinal centers or mantle zones provide appropriate microenvironments for cells carrying these oncogenic alterations to survive or proliferate. The progression of these lesions to overt lymphomas occurs rarely and may require the accumulation of additional genetic events. Individuals with these lymphoid proliferations should be managed with caution.

Lymphoid follicle colonization by Bcl-2(bright+)CD10(+) B-cells ("follicular lymphoma in situ") at nodal and extranodal sites can be a manifestation of follicular homing of lymphoma

Follicular lymphoma (FL) in situ (FLIS) was first described and proposed as a distinct entity associated with an indolent clinical course in 2002. To gain further insight into the biology of this enigmatic lymphoproliferation, we analyzed morphologic, phenotypic, cytogenetic and molecular features of tissue specimens manifesting a pattern of follicular colonization by Bcl-2(bright+)CD10(+) B-cells and associated lymphomas from 13 adults and evaluated their clinical outcomes. We observed this immunoarchitectural pattern in lymph nodes (n = 8), at extranodal sites (n = 4), or at both locations (n = 1) at diagnosis. All except 3 cases showed concomitant bright CD10 expression. Six (46%) patients had synchronous and 2 (15%) developed metachronous B-cell lymphomas, with 5 representing high-grade lymphomas. The Bcl-2(bright+)CD10(+) B-cells colonizing reactive follicles and synchronous lymphomas were clonally related in 4/5 (80%) cases analyzed and 5/6 (83%) displayed BCL2 translocations. Two cases exhibited complex karyotypes in both components; a genetic "triple hit" was detected in one instance and 2 copies of t(14,18) were observed in a lymph node biopsy lacking evidence of lymphoma from an individual with stage 4 disease, suspected on imaging, who subsequently displayed a mantle zone/perifollicular infiltrate of Bcl-2(bright+)CD10(+) B-cells in the adenoids. Our findings suggest that bright Bcl-2, and often bright CD10 expression, by B-cells colonizing reactive follicles might represent a phenomenon related to follicular homing of lymphoma, rather than being an attribute of preneoplastic FL precursors. Furthermore, due to the relatively high frequency of overt lymphomas observed, complete staging workup is recommended for patients exhibiting a Bcl-2(bright+)CD10(+) B-cell follicular colonization pattern on biopsy.

Nodal and leukemic small B-cell neoplasms

The small B-cell neoplasms represent some of the most frequently encountered lymphoproliferative disorders in routine surgical pathology practice. This report reviews the current diagnostic criteria for classifying small B-cell neoplasms and distinguishing them from newly recognized precursor conditions that do not appear to represent overt lymphomas. Newly available immunohistochemical stains and molecular studies that may assist in the diagnosis and classification of these neoplasms are also discussed.

In situ mantle cell lymphoma in the nasopharynx

BACKGROUND

Mantle cell lymphoma (MCL) is a B-cell neoplasm with an aggressive clinical course. Recently, an indolent type of MCL has been described under the term in situ MCL.

METHODS AND RESULTS

We report a case of a 70-year-old woman who presented with nasal obstruction. A mass, located in the nasopharynx, was found. Histologic examination revealed lymphoid hyperplasia characterized by CD5 and cyclin D1-positive mantle zone cells, findings consistent with in situ MCL. Three years later, a new biopsy was performed, which showed the same histologic and immunohistochemical (IHC) findings to those observed in the first biopsy. The diagnosis of in situ MCL was confirmed by fluorescence in situ hybridization (FISH) analysis for t(11;14). Since then, the patient has remained free of an overt lymphoma.

CONCLUSIONS

In situ MCL may be observed in the nasopharynx, and it would be appropriate to perform cyclin D1 immunostain in cases with marked follicular hyperplasia accompanied by clinical suspicion of lymphoma.

Mantle cell lymphoma as a component of composite lymphoma: clinicopathologic parameters and biologic implications

Composite lymphoma is a rare circumstance in which 2 or more distinct types of lymphoma occur in a single anatomical location. Although composite lymphoma has been increasingly identified with the advent of molecular genetic techniques, this topic has only rarely been a specific focus of the medical scientific literature. In this review, we focus on mantle cell lymphoma occurring as a major pathologic component of composite lymphoma and emphasize the clinicopathologic features of these tumors and associated biologic implications. To date, 26 cases of composite lymphoma including a component of mantle cell lymphoma have been previously published. Issues of clonal relatedness between the individual lymphoma components and emerging biologic implications as well as potential diagnostic pitfalls are evaluated.

"Intrafollicular neoplasia" of nodular lymphocyte predominant Hodgkin lymphoma: description of a hypothetic early step of the disease

The 2008 WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues has addressed the problem of intrafollicular neoplasia/"in situ" lesion for follicular lymphoma. The concept of intrafollicular neoplasia has also been proposed for other lymphomas in which the putative normal counterpart of the tumor cell is located in the germinal center or the mantle zone or the marginal zone of the follicle. However, unlike in situ follicular lymphoma, the precise histologic definition of this early lesion for other lymphomas is still lacking. When applied to nodular lymphocyte predominant Hodgkin lymphoma, another germinal center-derived lymphoma, "intrafollicular neoplasia" may be regarded as a neoplasia at an early stage of development, such as in situ follicular lymphoma. Interestingly, this early lesion can be observed in lymph nodes that otherwise show the most common nodular involvement by nodular lymphocyte predominant Hodgkin lymphoma. The recognition of intrafollicular neoplasia is based on the identification of typical, strongly stained BCL6+, lymphocyte predominant tumor cells located within altered follicles with a recognizable germinal center. Lymphocyte predominant tumor cells, surrounded by rosetting PD1+ T cells, reside in an environment reminiscent of a secondary follicle. Intrafollicular neoplasia in nodular lymphocyte predominant Hodgkin lymphoma is correctly identifiable based on immunohistochemical recognition of the CD23+ meshwork of follicular dendritic cells surrounded by an outer zone containing immunoglobulin D+ B cells. This immunoarchitectural pattern, highlighting the intrafollicular involvement by the neoplasia, is of great utility for diagnosis. An appropriate immunohistochemical characterization for diagnosis should include lymphocyte predominant (BCL6 and CD20) and microenvironmental (CD23, immunoglobulin D, and PD1) cell markers.

In situ follicular lymphoma associated with nonlymphoid malignancies

In situ follicular lymphoma (FL) is usually an incidental finding in otherwise reactive lymph node. This report describes two cases of lymph nodal in situ FL complicated by the association with nonlymphoid neoplasms. In case 1, in situ FL was discovered incidentally on a biopsy performed for an unexplained cervical lymphadenopathy 6 months after the resection of a carotid body paraganglioma. In case 2, in situ FL was detected incidentally during surgery for radical resection of prostatic carcinoma. In the lymph nodes, the in situ FL foci were characterized immunohistologically by strong coexpression of BCL2 and CD10 in the involved GCs. FISH study demonstrated BCL2 rearrangement in one of the two tested cases. These data extend the spectrum of the clinical situations that may be associated with in situ FL, but the biological and clinical significance of the association of in situ FL with nonlymphoid neoplasms deserves further investigation. Important fields of investigation should include: (1) how to approach these patients who have a risk of progression to overt lymphoma; (2) is the association of in situ FL with concurrent nonlymphoid neoplasia incidental, related to immunosuppression or to previous treatment?

Follicular lymphoma in situ: clinical implications and comparisons with partial involvement by follicular lymphoma

Follicular lymphoma in situ (FLIS) was first described nearly a decade ago, but its clinical significance remains uncertain. We reevaluated our original series and more recently diagnosed cases to develop criteria for the distinction of FLIS from partial involvement by follicular lymphoma (PFL). A total of 34 cases of FLIS were identified, most often as an incidental finding in a reactive lymph node. Six of 34 patients had prior or concurrent FL, and 5 of 34 had FLIS composite with another lymphoma. Of patients with negative staging at diagnosis and available follow-up (21 patients), only one (5%) developed FL (follow-up: median, 41 months; range, 10-118 months). Follow-up was not available in 2 cases. Fluorescence in situ hybridization for BCL2 gene rearrangement was positive in all 17 cases tested. PFL patients were more likely to develop FL, diagnosed in 9 of 17 (53%) who were untreated. Six patients with PFL were treated with local radiation therapy (4) or rituximab (2) and remained with no evidence of disease. FLIS can be reliably distinguished from PFL and has a very low rate of progression to clinically significant FL. FLIS may represent the tissue counterpart of circulating t(14;18)-positive B cells.

Does "in situ lymphoma" occur as a distinct step in the development of nodular lymphocyte-predominant Hodgkin lymphoma?

The concept of in situ neoplasia, already well acknowledged in epithelial tumors, has now been extended to lymphoid neoplasms. Among germinal center (GC)-derived lymphomas, a type of "in situ follicular lymphoma (FL)" has been described in which cells that strongly express BCL2 are observed in histologically abnormal follicles. In this commentary, the author suggests that another GC-derived lymphoma, ie, nodular lymphocyte-predominant Hodgkin lymphoma with a micronodular pattern in which small GCs or broken-up GCs are present within nodules, may be regarded as an early lesion limited to GC. Like "in situ FL," this is likely to be an in situ step that potentially leads to overt lymphoma.