Synchronous interdigitating dendritic cell sarcoma and B-cell small lymphocytic lymphoma in a lymph node.

A gradually enlarging axillary mass in a 79-year-old man was excised. The specimen was processed for light microscopy, immunohistochemical studies, and electron microscopy; gene rearrangement studies were also performed. A diagnosis of an interdigitating dendritic cell tumor of the lymph node and a B-cell small lymphocytic lymphoma occurring in the same anatomic location was made. We found that although rare cases of interdigitating dendritic cell tumor with an associated secondary malignancy have been described in the literature, to our knowledge, this is the first report of interdigitating dendritic cell tumor and synchronous neoplasm diagnosed at the same site. A possible relationship between the 2 disorders is also discussed.

CD117 expression in diffuse large B-cell lymphomas: fact or fiction?

CD117 (KIT) is expressed in a variety of hematopoietic neoplasms but there are a paucity of data regarding its expression in diffuse large B-cell lymphomas (DLBCL). The purpose of the present paper was to describe the authors' experience of two CD117+ DLBCL (one of follicle center-cell origin and one nasal Epstein-Barr virus (EBV)- plasmablastic lymphoma associated with lytic bone lesions), as determined by tissue immunohistochemistry and flow cytometry. The CD117 expression in DLBCL was further evaluated using tissue microarrays and seven additional plasmablastic lymphomas, using two commercially available anti-CD117 antibodies (Ab-1, Oncogene and A4502, DakoCytomation). Membranous +/- cytoplasmic staining was seen with Ab-1 in 24/65 (37%) DLBCL, including 21/56 microarray DLBCL, two index cases, and 1/7 additional plasmablastic lymphomas, with persistent staining in 13% of microarray DLBCL despite preincubation with KIT peptide. However, A4502 had only membranous staining of the index cases and one additional EBV- plasmablastic lymphoma with medullary disease. The present study suggests that (i) CD117 expression can be detected sporadically in DLBCL of follicle center-cell origin and a subset of plasmablastic lymphomas; (ii) staining for CD117 might help in identifying EBV- plasmablastic lymphomas associated with bone marrow involvement; and (iii) CD117 antibodies should be carefully validated prior to use, because non-specific staining, as observed with Ab-1, could lead to false-positive results.

Simultaneous occurrence of medullary and papillary carcinomas of the thyroid gland with metastases of papillary carcinoma to the cervical lymph nodes and the coinciding small B-cell lymphocytic lymphoma of the lymph nodes--a case report.

We report a case of a simultaneous occurrence of medullary and papillary carcinomas of the thyroid gland with metastases of a papillary carcinoma to the cervical lymph nodes and a concurrent small B-cell lymphocytic lymphoma revealed in the lymph nodes examined in a 71-year-old woman. The diagnosis was based on microscopic examination of surgical specimens and supported by immunohistochemistry. Additionally, P53 and RET mutation analysis was performed. In this case, the coincidence of medullary and papillary carcinomas of the thyroid gland may account for a true composite tumor. The coexistence of a small B-cell lymphoma in our patient may be explained by irradiation treatment undergone during the adolescence.

Comparison of immunophenotypes of small B-cell neoplasms in primary lymph node and concurrent blood or marrow samples.

Immunophenotyping of small B-cell neoplasms (SBCNs) may have a critical role in diagnosis. However, there are few data addressing whether the immunophenotypes of SBCNs in bone marrow (BM) and peripheral blood (PB) are representative of those in other tissue sites. We compared the immunophenotypic features of concurrently analyzed lymph node (LN) and BM/PB specimens using multiparameter flow cytometry. Fifty-five SBCNs were identified: 27 follicular lymphomas (FLs), 16 chronic lymphocytic leukemia/small lymphocytic lymphomas (CLL/SLLs), and 12 mantle cell lymphomas (MCLs). Major (presence vs absence) or minor (alteration of intensity) variations in expression of individual antigens between LN and BM/PB were observed in up to 25% of cases within a particular SBCN category. All FLs and CLL/SLLs maintained characteristic immunophenotypes in BM/PB. Potentially misleading variations included 1 case of MCL that failed to express CD5 in BM and likely would have been immunophenotypically misclassified as a marginal zone lymphoma and another MCL that expressed moderate CD23 in PB and would have required additional studies for precise classification. The remaining major and minor variations would not have affected interpretation.

Splenic small B-cell lymphoma with predominant red pulp involvement: a diffuse variant of splenic marginal zone lymphoma?

AIMS: Splenic marginal zone lymphoma (SMZL) has been characterized by a micronodular pattern of infiltration, biphasic cytology, follicular replacement and the presence of marginal zone differentiation. Here we describe four cases with some distinctive features, such as diffuse splenic infiltration, lack of micronodules, marginal zone cytology, p53 inactivation and cutaneous involvement. METHODS AND RESULTS: In the course of a review of cases of SMZL, we recognized the existence of a subset of four cases of splenic B-cell lymphoma, with predominantly red pulp involvement, absence of follicular replacement, and a monomorphous population of tumoral cells resembling marginal zone B-cells, with scattered nucleolated blast cells. The immunophenotype (bcl2+, CD5-, CD10-, CD43-, CD23-, cyclin D1-, IgD- (3/4)) was consistent with SMZL. Bone marrow infiltration (4/4) and peripheral blood involvement (2/4) showed similar findings to those described for SMZL in these locations. However, unlike classical SMZL, 2/4 had cutaneous involvement, and 4/4 cases showed either p53 mutation or anomalous p53 staining (p53+, p21-). CONCLUSIONS; In spite of a diffuse pattern of splenic infiltration, cutaneous involvement and p53 alterations, these cases have findings that overlap with those corresponding to classic SMZL (symptomatology, morphology of bone marrow, lymph nodes, peripheral blood involvement, and immunophenotype). We suggest that these cases be considered a putative variant of SMZL.

Anetoderma arising in cutaneous B-cell lymphoproliferative disease.

Anetoderma is circumscribed atrophy of the skin due to a localized deficiency in elastic tissue. It can follow inflammatory skin diseases of several types, and occasionally is present in the skin around neoplasms. There are a few reports of anetoderma in the lesional skin of cutaneous lymphoma. We report on two patients who presented with multiple lesions of anetoderma and who later proved to have low-grade cutaneous B-cell lymphomas. One patient (Patient 1) is a 39-year-old man and the other patient is a 26-year-old woman who is a renal transplant recipient (Patient 2). Some biopsy specimens from the anetodermic skin of Patient 1 appeared to show an urticarial reaction, although plasma cells were present. A large nodule showed lymphoid follicles surrounded by plasmacytoid lymphocytes, with loss of elastic tissue in the adjacent dermis. The plasmacytoid cells stained overwhelmingly for lambda light chain, and staining of the urticarial lesions from this patient also showed a marked majority of lambda positive cells. Immunoglobulin heavy chain gene (IgH) rearrangements showed a dominant clonal pattern in the nodular lesion. We classified the disease in Patient 1 as marginal zone lymphoma and the disease in Patient 2 as a post-transplant lymphoproliferative disorder. Because of the intimate association of anetoderma and cutaneous B-cell lymphoproliferative disorders in these two patients, it seems possible that anetoderma could result from either a local effect of the neoplastic cells or associated inflammatory cells, especially neutrophils as in Case 1. The infiltrates of Case 1 had many interstitial neutrophils and only a few clonal plasmacytoid lymphocytes, indicating that this presentation of B-cell lymphoma can be a diagnostic pitfall. Given these two cases and similar ones in the literature, biopsy of lesional skin in anetoderma should be performed to ensure that lymphomatous infiltrates are not present. Even if plasma cells are sparse, studies to detect clonality are appropriate. Cutaneous B-cell lymphoma can be added to the list of associations of elastolysis and cutaneous lymphoma, which includes granulomatous slack skin (T-cell lymphoma) and cutis laxa (myeloma).

Value of CD23 determination by flow cytometry in differentiating mantle cell lymphoma from chronic lymphocytic leukemia/small lymphocytic lymphoma.

Mantle cell lymphoma (MCL) and chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) share many morphologic and immunophenotypic features. In addition to histomorphologic examination, it is customary to use the absence of CD23 to differentiate MCL from CLL/SLL, based primarily on reported comparisons of immunohistochemical staining of tissue sections. These findings are widely extrapolated to flow cytometric analysis, although available data are contradictory and not sufficiently detailed. We compared expression of CD23 by flow cytometry in 22 cases of MCL and 25 cases of CLL/SLL. Lymphoma cells in 12 of 22 MCLs were negative for CD23, and 10 showed dim expression. In contrast, none of 25 CLL/SLLs were negative for CD23, 4 were dimly positive, and 21 were moderately or brightly positive. Thus, a significant proportion of MCL exhibited overlap of CD23 expression in the low-intensity range with CLL/SLL. Clinically, there was no correlation between the intensity of CD23 expression and clinical stage at diagnosis or survival. These findings emphasize that by flow cytometry, MCL can be differentiated reliably from CLL/SLL using CD23 if negative expression is observed. However, with dimly positive expression, interpretation should be cautious.

Analysis of the immunoglobulin heavy chain gene of secondary diffuse large B-cell lymphoma that subsequently developed in four cases with B-cell chronic lymphocytic leukemia or lymphoplasmacytoid lymphoma (Richter syndrome).

The immunoglobulin heavy chain gene (IgH gene) was analysed in four cases of B-cell Richter syndrome, in order to determine whether a secondary diffuse large B-cell lymphoma (DLBCL) could arise from the same clone as the initial B-cell chronic lymphocytic leukemia (B-CLL) and lymphoplasmacytoid lymphoma (LPL) or be a de novo event, and whether secondary DLBCL shows an intraclonal microheterogeneity. Both the initial B-CLL and secondary DLBCL in two cases expressed CD5 antigen. Both samples of the initial B-CLL or LPL and the secondary DLBCL in three cases were examined for comparison. The polymerase chain reaction-amplified IgH gene of secondary DLBCL in two cases (CD5+ case and CD5- case) were different from those of the initial B-CLL, revealing a new malignant clone. The other case (CD5-) showed that secondary DLBCL had a sequence identical to the initial LPL, indicating the same clonal origin. The variable region of the IgH gene of secondary DLBCL (CD5+ two cases and CD5- two cases) exhibited a 0.5-9.0% somatic mutation range and no intraclonal microheterogeneity.

Signet-ring cell variant of small lymphocytic lymphoma with a prominent sinusoidal pattern.

Signet-ring cell lymphoma is a rare morphologic variant of non-Hodgkin's lymphoma characterized by neoplastic lymphoid cells with cytoplasmic vacuoles or eosinophilic globules that impart a signet-ring cell morphology. Although most cases are variants of follicular center B-cell lymphomas, this pattern also can be seen in T-cell lymphomas. An indolent clinical course and prolonged survival have characterized the majority of published cases. We document the case of a 62-year-old African-American woman with diffuse small lymphocytic signet-ring lymphoma having a predominant sinusoidal growth pattern, which, to our knowledge, has not been previously reported. The prominent sinusoidal pattern of signet-ring lymphocytes contributes to its confusion with metastatic signet-ring cell adenocarcinoma. The correct diagnosis is greatly facilitated by the use of appropriate immunohistochemical stains for lymphoid markers.

Transformation of the small cell variant Ki-1+ lymphoma to anaplastic large cell lymphoma: pathologic and clinical features.

The disease spectrum of anaplastic large cell lymphoma (ALCL) includes a biologically aggressive small cell variant (SCV). The SCV may progress to ALCL, but little is known about the transformation process and its significance. The goals of this study were (1) to identify the clinical and pathologic features that characterize ALCL arising in SCV and (2) to determine whether some cases with ALCL histologic appearance at the outset arose from an SCV. Seventeen SCV were reviewed, and four cases (24%) transformed to ALCL as shown by subsequent biopsy. The ALCLs were predominantly monomorphic (3 cases) rather than pleomorphic (1 case). Residual SCV was detected at transformation in 3 of 4 cases. Twenty-one de novo T-cell ALCLs were reviewed for an SCV component; such a component was identified in two ALCLs with monomorphic features, suggesting a preceding SCV phase. There was no change in the immunophenotype between the SCV and ALCL, all marking as EMA+ T cells. Expression of p80 was detected in 3 of 4 (75%) SCV with transformation and 10 of 12 (77%) SCV without transformation. Chromosomal abnormalities involving the sex chromosomes and 6, 7, 9, and 15, in addition to the characteristic t(2;5)(p23;q35), were present in 2 cases at transformation. Times to transformation ranged from 1 to 146 months (mean: 63 months) after diagnosis. Transformation to ALCL signaled a rapid clinical course, with 75% of patients dying in less than a year; one patient remains alive at 15 months. In summary, some ALCLs, particularly those with monomorphic features, arise from an SCV. Transformation to ALCL signals a rapid course, with death occurring in less than a year in most cases. Necrosis in the SCV may be predictive of transformation. Chromosomal abnormalities in addition to the t(2;5)(p23;q35) are present at transformation, suggesting that multiple genetic alterations are involved in disease progression.

Primary cutaneous marginal zone B-cell lymphoma: a recently described entity of low-grade malignant cutaneous B-cell lymphoma.

Recently a new classification of primary cutaneous B-cell lymphomas (PCBCLs) has been proposed by the European Organization for Research and Treatment of Cancer (EORTC)--Cutaneous Lymphoma Project Group. The marginal zone B-cell lymphomas (MZLs) were not included as a distinct entity because of insufficient experience and controversial opinions. We have studied 32 patients (M:F ratio 1.5:1; age range 25-93 years; mean age 49.6 years; median age 50 years) to determine the diagnostic criteria of primary cutaneous MZL and the relationship with other low-grade malignant PCBCLs. For comparison, three patients with immunocytoma were included in the study. Clinically, patients presented with solitary or clustered reddish or red-brown papules, nodules, and plaques, sometimes surrounded by an erythematous halo. Histopathologic sections showed nodular or diffuse infiltrates involving the dermis and subcutaneous fat. Cytomorphologically small to medium-sized cells with indented nuclei and abundant pale cytoplasm (marginal zone cells, centrocyte-like cells) predominated. In addition, scattered blasts, lymphoplasmacytoid cells, and plasma cells were observed below the epidermis and at the periphery of the infiltrates. Reactive germinal centers were present in 75% of the cases. The three cases of immunocytoma showed a more monomorphous pattern with predominance of lymphoplasmacytoid cells. The marginal zone cells showed a CD20+, CD79a+, CD5- and Bcl-2+ immunophenotype. They expressed immunoglobulin G in the majority of the cases. Staining with the monocytoid B cell-related antibody KiM1p gave positive results in all specimens with a typical intracytoplasmic granular pattern. A monoclonal distribution of immunoglobulin light chains was observed in marginal zone cells in 75% of the cases. Germinal centers, when present, were either polyclonal or negative for both kappa and lambda light chains. Monoclonal rearrangement of the JH gene was detected via polymerase chain reaction (PCR) in 18 of 26 investigated specimens. Analysis in 12 patients of the bcl-2/immunoglobulin heavy chain gene rearrangement using PCR yielded negative results. Lesions were treated by surgical excision followed in some patients by local radiotherapy. Systemic antibiotic therapy was administered to three patients, with good response in two. The prognosis is excellent. After a mean follow-up of 47.9 months (range 6-252; median 24) all patients are alive without signs of systemic lymphoma. Primary cutaneous MZL represents a distinct clinicopathologic subtype of low-grade malignant PCBCL.

Cyclin D1 immunohistochemical staining is useful in distinguishing mantle cell lymphoma from other low-grade B-cell neoplasms in bone marrow.

The distinction between mantle cell lymphoma (MCL) and other low-grade B-cell neoplasms is important because MCL has a more aggressive clinical course. In bone marrow biopsy specimens, this distinction can be especially difficult. We examined 70 bone marrow biopsy specimens involved by various B-cell lymphoid neoplasms to assess the utility of cyclin D1 immunostaining in distinguishing MCL from other B-cell lymphoproliferative disorders. We used a cocktail of two monoclonal anti-cyclin D1 antibodies and a heat- and sonication-induced epitope retrieval procedure. The neoplasms assessed included MCL (32 cases), small lymphocytic lymphoma/chronic lymphocytic leukemia (18 cases), follicular lymphoma (11 cases), hairy cell leukemia (5 cases), splenic marginal zone lymphoma (2 cases), and small lymphocytic lymphoma with plasmacytoid differentiation (2 cases). The diagnosis of MCL in bone marrow was confirmed by review of the original diagnostic biopsy specimens along with additional data, such as immunophenotypic or molecular studies. Most MCL (23/32; 72%) cases expressed cyclin D1 protein. In contrast, one case of small lymphocytic lymphoma/chronic lymphocytic leukemia (1/18; 6%) and one case of hairy cell leukemia (1/5; 20%) expressed cyclin D1 protein. These findings demonstrate that immunostaining for cyclin D1 protein expression is useful in distinguishing MCL from other B-cell lymphoid neoplasms in the bone marrow.

Amyloidoma of bone, a plasma cell/plasmacytoid neoplasm. Report of three cases and review of the literature.

Tumoral amyloidosis (amyloidoma) of bone is a rare condition characterized by the massive destructive deposition of AL amyloid in bones. We report three cases. The patients ranged in age from 45 to 78 years and had tumors located in the lumbar spine, scapula, and humeral head measuring 6.5 to 18 cm. The radiologic diagnosis was chondrosarcoma in two cases. Microscopically, there were large, rounded deposits of amorphous eosinophilic material surrounded by numerous giant cells and a sparse lymphoplasmacytic infiltrate. The deposits proved to be composed of AL amyloid showing potassium permanganate resistant congophilia. Immunohistochemistry showed immunoglobulin IgG lambda, IgG kappa, and IgM lambda monoclonality of the plasma cell and (in one case) lymphoid infiltrate. The tumors were classified by morphology and immunohistochemistry as solitary plasmacytomas of bone (two cases) and plasmacytoid lymphoma (one case). During the relatively short follow-up period, one patient progressed to symptomatic generalized amyloidosis and died, one patient died of recurrent tumor, and one patient is alive with no evidence of disease. An extensive review of the world literature showed 34 well-documented similar cases, occurring most often in the spine and skull, causing neurologic symptoms, tending to occur in middle-aged men and frequently progressing to generalized disease. Most if not all AL amyloidomas of bone represent solitary plasmacytomas of bone or plasmacytoid lymphomas.

Primary intracerebral small lymphocytic non-Hodgkin's lymphoma with plasmacytoid differentiation, associated with prominent extracellular proteinaceous deposits.

A case of primary intracerebral non-Hodgkin's lymphoma in a 67-yr-old immunocompetent female is presented. The histopathological diagnosis was supported by immunohistochemical, flow cytometric and electron microscopic findings, and by clinical staging. This tumor is unusual in its morphological features of a low grade, small lymphocytic lymphoma with plasmacytoid differentiation (Working Formulation Classification), and its association with extensive, local, extracellular, proteinaceous deposits. Primary central nervous system non-Hodgkin's lymphomas are briefly discussed and it is postulated that the extracellular proteinaceous deposits in this case originated from immunoglobulins secreted by the neoplastic cells. To our knowledge the massive degree of local immunoglobulin deposition present in this primary central nervous system lymphoma has not been previously reported in the literature.

Cyclin D1 (Bcl-1, PRAD1) protein expression in low-grade B-cell lymphomas and reactive hyperplasia.

Mantle cell (centrocytic) lymphoma (MCL) and occasional cases of B-cell small lymphocytic lymphoma/chronic lymphocytic leukemia (B-SLL/CLL) show a characteristic translocation, t(11:14)(q13;q32) involving rearrangement of the Bcl-1 region. Recently it was shown that the key Bcl-1 region oncogene is cyclin D1/PRAD1; cyclin D1 mRNA was shown to be overexpressed in cases of MCL. We examined cyclin D1 protein expression in low-grade B-cell lymphomas and reactive lymphoid hyperplasias using polyclonal and monoclonal antibodies to cyclin D1 protein. Definite nuclear staining was seen in 15 of 15 MCLs, 1 of 7 B-SLL/CLLs, 0 of 7 reactive hyperplasias, 0 of 10 follicular lymphomas, and 0 of 4 lymphomas of mucosa-associated lymphoid tissue using immunoperoxidase stains on paraffin-embedded sections. Best results were obtained with the affinity-purified polyclonal antibody on microwave-treated, formalin-fixed, paraffin-embedded tissue. MCLs showed diffuse nuclear staining, whereas the one positive B-SLL/CLL showed dot-like or globular nuclear staining. Nuclear cyclin D1 protein can be detected in all cases of MCL and in rare cases of B-SLL/CLL using an immunohistochemical technique on formalin-fixed, paraffin-embedded tissue, and it does not appear to be detectable in reactive hyperplasias and other low-grade B-cell lymphomas. This protein may be useful in subclassification of low-grade B-cell lymphomas.

bcl-2 protein expression and correlation with the interchromosomal 14;18 translocation in cutaneous lymphomas and pseudolymphomas.

The interchromosomal 14;18 translocation occurs in approximately 70-80% of follicular lymphomas and in a lower proportion of high-grade non-Hodgkin lymphomas of the lymph nodes. This translocation results in the fusion of the bcl-2 oncogene on chromosome 18 with immunoglobulin heavy chain genes on chromosome 14, and in the expression of higher amounts of normal bcl-2 protein. We studied bcl-2 expression in biopsies of 108 patients with benign and malignant cutaneous lymphoproliferative diseases (B-cell lymphoma, primary cutaneous, 42; secondary cutaneous, 21; primary cutaneous T-cell lymphoma, 21; B-cell pseudolymphoma, 24), using a monoclonal anti-bcl-2 antibody on paraffin-embedded tissue sections, bcl-2 protein was detected immunohistochemically in 16 of 63 cases of cutaneous B-cell lymphoma, whereas cutaneous T-cell lymphomas and B-cell pseudolymphomas were negative. The proportion of bcl-2 protein expression was significantly higher in secondary (11/21) than in primary cutaneous B-cell lymphomas (5/42; chi 2 test, p < 0.001). Biopsies from 25 of these patients (B-cell lymphoma, 22; B-cell pseudolymphoma, three) were analyzed previously on the molecular level for the t(14;18), using polymerase chain reaction amplification of DNA obtained from paraffin-embedded sections. In four of 11 cases of bcl-2 protein-positive B-cell lymphoma (primary, one; secondary, three) the t(14;18) was detected by polymerase chain reaction. All other cases of B-cell lymphoma, including seven cases where bcl-2 protein was detected by immunohistology, and B-cell pseudolymphoma were negative. These results demonstrate: 1) bcl-2 protein is expressed in a small portion of cutaneous B-cell lymphomas; 2) bcl-2 protein expression is significantly more frequent in secondary than in primary cutaneous B-cell lymphoma; 3) only approximately one-third of cases expressing the bcl-2 protein are characterized also by the t(14;18). bcl-2 protein expression might indicate that the cutaneous manifestation of the lymphoma represents a secondary spread from a node-based lymphoma.

Detection of Epstein-Barr virus genome in primary cutaneous T and B cell lymphomas and pseudolymphomas.

The Epstein-Barr virus (EBV) genome has recently been identified in Hodgkin's disease (HD) and nodal non-Hodgkin's lymphomas (NHL). In order to elucidate the possible aetiopathogenetic role of EBV in benign and malignant lymphoproliferative disorders we investigated skin specimens from 24 patients with a primary cutaneous lymphoproliferative disorders (10 T-cell lymphomas 6 B-cell lymphomas and 8 pseudolymphomas) and from 22 normal individuals for the presence of EBV DNA using the polymerase chain reaction (PCR) technique and in situ hybridization (ISH) on formalin-fixed paraffin-embedded tissue sections. EBV DNA was identified by PCR in one of two cases of mycosis fungoides, in one of seven cases of pleomorphic T-cell lymphomas, in one case of centroblastic (CB) lymphoma of six B-cell lymphomas, and in three of eight pseudolymphomas. The EBV genome was also found in 2 of 22 specimens of normal skin. The small EBV-encoded nuclear RNAs, EBERs, were not detected in any PCR-positive sample by ISH. Based on our PCR and ISH findings, EBV does not seem to play a significant role in the development of cutaneous lymphomas.

Immunoglobulin-producing tumours in dogs and cats.

Tumours with a plasmacytoid pattern taken from 32 dogs and four cats were examined for the presence of immunoglobulins, which would allow them to be designated as B-cell lymphomas. Within a total of 19 immunoglobulin-positive tumours, three types could be distinguished: extramedullary plasmacytoma (15), multiple myeloma (two) and immunocytoma (two). These tumours occurred in 18 of the dogs, and in one cat (extramedullary plasmacytoma). The characteristics of the immunoglobulin-producing tumours were investigated by light and electron-microscopy as well as by immunohistochemical methods. Seventeen of the 19 tumours expressed lambda-type light chains and one tumour kappa-type light chains. Heavy chains were also synthesized by five tumours.

Clonal heavy chain isotype switching within the proliferation centers of a small lymphocytic lymphoma: implications regarding the origin of proliferation centers.

We describe an unusual case of small lymphocytic lymphoma with multiple prominent pseudofollicular proliferation centers in which immunohistochemistry reveals that the small cells are surface IgM kappa positive and the large pseudofollicular cells are surface IgA kappa positive. We further show by genomic DNA analysis that the tumor tissue contains two JH rearrangements, one Cmu rearrangement, one C alpha rearrangement, and a single C kappa rearrangement, strongly suggesting that the large cells within the proliferation centers have arisen from the small cells via a clonal heavy chain immunoglobulin isotype switch. Isotype switching in human lymphoma and leukemia appears to be an uncommon event. However, there are reports that strongly support isotype switching in pre-B-cell leukemia, Richter's syndrome, lymphoid blast crisis of chronic myelogenous leukemia, and multiple myeloma. To our knowledge, there have been no previous reports demonstrating isotype switching within the proliferation centers of small lymphocytic lymphoma. We present evidence of in vivo intratumoral isotype switching within the proliferation centers of a small lymphocytic lymphoma documented at the level of immunohistochemistry and DNA rearrangement.

Purification and partial characterization of 200 kDa oncofetal antigen from radiation induced murine lymphocytic lymphoma.

1. A 200 kDa glycoprotein (gp200) oncofetal antigen was purified from solubilized membranes of a radiation-induced murine lymphocytic lymphoma cell line (XR11-5T), grown in syngeneic RFM mice, by successive gel chromatography of the active fraction on lentil lectin agarose, Q- and S-Sepharose and Superose-12 using an FPLC system. 2. A murine monoclonal antibody 115, produced by the syngeneic immunization of adult male C57BL/6N mice with 12-day mouse fetal cells, was used in a slot blot antibody assay to follow up the active fractions. 3. The purified glycoprotein has a pI of 5.4. 4. Treatment of radiolabeled gp200 with neuraminidase caused a slight reduction in size due to the removal of sialic acid groups and a shift in pI to 6.3. 5. Treatment of gp200 with different glycosidases shows that gp200 is susceptible to N- and O-glycanase but not to endoglycosaminidase H. 6. On extraction of gp200 with Triton X-114 it partitions exclusively into the detergent-rich fraction consistent with being an integral membrane protein.