Differential expression of enhancer of zeste homolog 2 (EZH2) protein in small cell and aggressive B-cell non-Hodgkin lymphomas and differential regulation of EZH2 expression by p-ERK1/2 and MYC in aggressive B-cell lymphomas.

EZH2, a member of the polycomb protein group, is an important methyltransferase that is overexpressed in various neoplasms. We found that in small cell B-cell lymphomas, EZH2 is expressed in <40% of neoplastic cells, with heterogenous signal intensity. In aggressive B-cell lymphomas, 70-100% of tumor cells were positive for EZH2 expression with high signal intensity, which correlated with a high proliferation rate. We investigated the potential signaling molecules that regulate EZH2 overexpression in aggressive B-cell lymphomas and found that 80% of cases of EZH2-positive diffuse large B-cell lymphoma show high p-ERK1/2 expression (average ~57% tumor cell positivity). In contrast, only a small percentage of tumor cells (~10%) show p-ERK1/2 expression in Burkitt lymphoma and double hit lymphoma. On average, 91 and 76% of neoplastic cells were positive for MYC expression in Burkitt lymphoma and double hit lymphoma, respectively, while only 20% neoplastic cells were positive for MYC expression in diffuse large B-cell lymphoma. None of the aggressive B-cell lymphomas showed significant p-STAT3 expression in EZH2-overexpressed cases. The correlation of EZH2 expression with aggressive behavior and proliferation rate in B-cell neoplasms suggests that this molecule may function as an oncogenic protein in these neoplasms, with possible regulation by different signaling cascades in different types of aggressive B-cell lymphomas: p-ERK-related signaling in diffuse large B-cell lymphoma, and MYC-related signaling in Burkitt lymphoma and double hit lymphoma. Furthermore, EZH2 and associated signaling cascades may serve as therapeutic targets for the treatment of aggressive B-cell lymphomas.

Enhancer of zeste homolog 2 is widely expressed in T-cell neoplasms, is associated with high proliferation rate and correlates with MYC and pSTAT3 expression in a subset of cases.

Enhancer of zeste homolog 2 (EZH2), an epigenetic regulator and H3k27-specific histone methyltransferase, is important for transcriptional regulation. EZH2 has been found to be overexpressed in B-cell lymphomas, as well as some T-cell lymphomas. Here we investigated the expression of EZH2 by immunohistochemical staining in a wide range of T-cell neoplasms. We found that EZH2 is highly expressed in all categories of T-cell neoplasia studied, and its expression strongly correlates with a high proliferation rate. Although up-regulation of EZH2 has been reported to be modulated by the pSTAT3-MYC pathway, our data indicate that EZH2 expression is correlated with MYC and/or pSTAT3 expression in only a subset of T-cell lymphomas, and that other mechanisms may control the overexpression of EZH2 in many T-cell lymphomas. The high level of EZH2 expression in T cell lymphomas suggest that these neoplasms may benefit from targeted treatment with a small molecule inhibitor of EZH2 currently in use in clinical trials.

Imatinib mesylate lacks efficacy in relapsed/refractory peripheral T cell lymphoma.

Platelet derived growth factor-α (PDGFR-α) is expressed in peripheral T cell lymphoma, not otherwise specified (PTCL, NOS). Imatinib mesylate demonstrated in vitro cytotoxicity against primary PTCL, NOS cells. We initiated a trial of imatinib in 12 patients with relapsed or refractory T-cell non-Hodgkin lymphoma (T-NHL). PDGFR-α expression by immunohistochemistry and fluorescence in situ hybridization (FISH) to assess for FIP1L1-PDGFR-α fusion and/or PDGFR-α amplification were not required for study entry. We documented no objective responses. The median progression-free survival was 21.0 days (90% confidence interval [CI] 15.0, 28.0) and median overall survival was 154 days (90% CI 35, 242). Four patients had tissue available for analysis of PDGFR-α by immunohistochemistry and three of these patients' tumors expressed PDGFR-α. Imatinib was not effective for the treatment of peripheral T cell lymphoma in an unselected group of patients in which PDGFR-α expression was not required for study entry.

Patterns of expression of CD56 and CD117 on neoplastic plasma cells and association with genetically distinct subtypes of plasma cell myeloma.

Plasma cell neoplasms are common hematopoietic malignancies that recently have been shown to be driven by specific genetic events. In the past decade, immunophenotyping by flow cytometry has become an important tool in the characterization of plasma cells. However, the clinical and prognostic significance of antigenic expression remains unclear. We analyzed 102 cases of plasma cell neoplasm by flow cytometric immunophenotyping for expression of CD56 and CD117 and correlated the results with immunohistochemical and cytogenetic findings. Expression of CD56 and CD117 was associated with hyperdiploidy and the absence of CD117 expression was associated with different immunoglobulin heavy chain gene (IGH) translocations. Assessment of CD117 expression on neoplastic plasma cells by flow cytometry is superior to immunohistochemistry. Simultaneous assessment of CD56 and CD117 expression by flow cytometry is a sensitive method for diagnostic evaluation of plasma cell neoplasms, and furthermore may function as a rapid adjunctive test providing independent prognostic information in the absence of cytogenetic data.

MUC expression in hyperplastic and serrated colonic polyps: lack of specificity of MUC6.

Previous studies have shown that hyperplastic and serrated polyps of the colon show variable degrees of gastric and intestinal differentiation. MUCs are a class of approximately 20 genes that encode high-molecular-weight glycoproteins, or mucopolysaccharides, that are widely expressed in epithelial cells and show organ specificity. The role of MUC in serrated carcinogenesis is unknown. One previously published study suggested that expression of MUC6 is specific for sessile serrated adenoma/polyps (SSA/Ps) and thus can be used to distinguish these lesions from hyperplastic polyps (HPs). However, data from our group suggest that MUC antibodies are not reliable in this differential diagnosis. The aims of this study were to systematically evaluate the expression of MUCs in serrated colon polyps and to determine the efficacy of MUC expression in differentiating HPs from SSA/Ps specifically. Routinely processed specimens from 182 serrated polyps [58 HPs, 46 SSA/Ps, 59 SSA/Ps with dysplasia (SSA/P-D), 19 traditional serrated adenomas, and 38 conventional tubular or tubulovillous adenomas (CAs)] were immunohistochemically stained with MUC1, MUC2, MUC5AC, and MUC6, and scored for extent, intensity, and location of staining within the polyps. HPs were further subclassified into goblet cell type (N=18), microvesicular type (N=21), and mucin-depleted type (N=19). The data were compared between the different polyp groups and between polyps from different anatomic locations in the colon. MUC1, MUC2, MUC5AC, and MUC6 were expressed in 27%, 100%, 100%, and 72% of serrated polyps overall. These antibodies were positive in 32%, 100%, 100%, and 43% of CAs. Expression levels of MUC1, MUC2, and MUC5AC were not significantly different between any of the polyp subgroups or between serrated polyps and CAs. Both SSA/P and SSA/P-D showed a significantly higher percentage of polyps that stained with MUC6, and a greater degree and intensity of staining for this peptide in comparison with HPs. Overall, 91% of SSA/Ps and 84% of SSA/P-Ds were positive for MUC6 in comparison with 60% of HPs (P<0.001 and P=0.02, respectively). Although polyps from both the left and right colon from each polyp group showed positivity for MUC6, a significantly higher proportion of SSA/P-Ds and traditional serrated adenomas from the right colon showed MUC6 positivity compared with those from the left. No differences were noted in MUC6 staining between each of the 3 HP subgroups. On the basis of these data, we conclude that SSA/P and SSA/P-D show increased expression of MUC6 compared with HPs; however, because of overlap in the presence, degree, and intensity of staining, use of MUC6 to differentiate HPs from SSA/P or SSA/P-D in individual cases is not reliable because of a lack of specificity. Differences in MUC6 expression between right-sided and left-sided colonic polyps supports the theory that there may be biological differences in the progression of malignancy in different portions of the colon with regard to the serrated pathway of carcinogenesis.

BAFF-R, the major B cell-activating factor receptor, is expressed on most mature B cells and B-cell lymphoproliferative disorders.

B cell-activating factor receptor (BAFF-R) is one of three known receptors for BAFF, a critical regulator of B- and T-cell function. In mice, BAFF-R is required for B-cell maturation and survival, and in mice and humans, the overproduction of BAFF is associated with autoimmune disease. We sought to determine the normal pattern of BAFF-R expression at specific stages of B- and T-cell development and whether this pattern of expression corresponds with related B- and T-cell neoplasms. Most circulating human B cells and a small subset of T cells are BAFF-R-positive. In reactive lymphoid tissues, BAFF-R is expressed by B cells colonizing the mantle zones, by a subset of cells within germinal centers, and rare cells in the interfollicular T-cell zone. BAFF-R is also expressed by B cells colonizing the splenic marginal zone. Seventy-seven (78%) of 116 cases of B-cell lymphoproliferative disorders were BAFF-R-positive by immunohistochemical and/or flow cytometric immunophenotypic analysis, including most cases of mantle cell lymphoma, follicular lymphoma, marginal zone lymphoma, chronic lymphocytic leukemia, hairy cell leukemia, and diffuse large B-cell lymphoma. In contrast, cases of precursor B lymphoblastic lymphoma, Burkitt lymphoma, and nodular lymphocyte-predominant Hodgkin lymphoma exhibit weak to negative staining for BAFF-R. All cases of classical Hodgkin lymphoma and T-cell lymphomas were BAFF-R-negative, including all cases of anaplastic large cell lymphoma, adult T-cell leukemia/lymphoma, angioimmunoblastic T-cell lymphoma, and peripheral T-cell lymphoma, unspecified. These findings highlight BAFF-R as a marker of both normal and neoplastic B cells and raise the possibility that BAFF-R expression is necessary for the survival of a subset of neoplastic B lymphocytes analogous to its known role in promoting normal B-cell maturation and survival.

Inflammatory fibroid polyps of the gastrointestinal tract: evidence for a dendritic cell origin.

Inflammatory fibroid polyps (IFPs) are rare mesenchymal tumors of the gastrointestinal tract that consist of spindle-shaped stromal cells and an inflammatory infiltrate rich in eosinophils. Their etiology and histogenesis remain unknown. Based on previous reports of their immunoreactivity for CD34 and c-kit biomarkers, IFPs have been thought to be related to gastrointestinal stromal tumors (GISTs). After reviewing the current literature and examining IFPs at the light microscopic level, we evaluated a series of IFPs using an extensive panel of immunohistochemical and in situ hybridization markers in an effort to gain insight into their etiology and histogenesis and to determine their true relationship to GISTs. Sixteen routinely processed IFP specimens (14 gastric, 1 ileal, and 1 rectal) were immunohistochemically stained for antibodies to CD34, HMB-45, desmin, smooth muscle actin, calponin, h-caldesmon, anaplastic lymphoma kinase, S-100 protein, epithelial membrane antigen, c-kit (CD117), stem cell factor (SCF/N19 or kit ligand), p53, bcl-2, cyclin D1, and human herpesvirus-8 (HHV8). In situ hybridization for Epstein-Barr virus-encoded RNA (EBER) was also performed. Ten cases were further evaluated for the dendritic cell markers fascin, CD21, CD23, and CD35. Stromal cells were diffusely positive for CD34 and fascin in all (100%) cases, and these stromal cells were, in addition, immunoreactive for calponin and smooth muscle actin in 88% and 25% of cases, respectively. CD35 was also found to be focally reactive in the stromal cells. Cyclin-D1 was overexpressed in all (100%) IFPs. All other immunohistochemical markers and EBER were negative in the stromal cells. These findings suggest that the proliferating stromal cells in IFPs are of dendritic cell origin, with some cases also exhibiting myofibroblastic features. Absence of c-kit, SCF, and h-caldesmon immunoreactivity fails to support a relationship to GISTs. We also conclude that Epstein Barr virus and HHV8 are unlikely etiologic agents of IFPs. Overexpression of cyclin D1 in all cases suggests that a defect in cell-cycle regulation may be involved in the growth of IFPs.