Scrotal skin ulcer in a patient with a previous tonsillectomy because of natural killer cell lymphoma

The CD56+ lymphomas are a recently characterized high-grade malignancy of putative natural killer cell origin. They are mostly localized to the nasal areas but show a propensity to spread to or recur in the skin. We describe a unique case of CD56+ natural killer lymphoma that recurred in scrotal skin in a patient 8 years after an initial limited resection. Although this case was unusual in showing a prolonged period of apparent remission, it illustrated a characteristic clinicopathologic behavior of this rare tumor.

Mantle cell lymphoma in the Chinese: clinicopathological features and treatment outcome

We report the clinical, molecular, and immunohistological findings of 20 Chinese patients with mantle cell lymphoma diagnosed over a 10-year period. The disease affected mainly elderly patients (median age, 65.5 years) with a male predominance (M/F, 3/1). Eighty percent presented with advanced stage III/IV disease but only 25% had B symptoms. Eighty-five percent had extranodal disease at presentation. Complete remission (CR) and partial remission (PR) were achieved in 45% and 40% of the patients, respectively. There was no difference in the CR rate for patients treated with anthracycline-containing or nonanthracycline-containing regimens (43% and 50%, P = 0.67). Disease progression or relapse was observed after a median of 26 months in patients who initially responded to treatment. Extranodal relapse occurred in the central nervous system (n = 1), bone marrow (n = 1), pleura (n = 2), orbit (n = 2), and the gastrointestinal tract (n = 3). The median overall survival (OS) was 52 months but there were no long-term survivors. This was not different from the median OS of 53 months of patients with diffuse large cell (DLC) lymphoma treated in the same center over the same period (log rank, P = 0.76). Of the 12 patients who were tested for bcl-1 rearrangement by polymerase chain reaction (PCR), five (42%) were positive for rearrangement in the major translocation cluster (MTC) region. The median OS rates were 45 months and 63 months for PCR positive and negative patients, respectively (P = 0.97). In conclusion, MCL is a disease mainly of the elderly in the Chinese with a male predominance and most had advanced-stage disease and extranodal involvement at presentation. Clinicopathologic features and treatment outcome were similar to Caucasian patients, in that the disease combined the aggressive nature of DLC lymphoma and the incurability of low-grade lymphoma.

Epstein-Barr virus infection and its gene expression in gastric lymphoma of mucosa-associated lymphoid tissue

The role of Epstein-Barr virus (EBV) in the pathogenesis of gastric lymphoma of mucosa-associated lymphoid tissue (MALT) has not been well understood. The aim of the study was to investigate EBV infection and its gene expression in this tumor in order to understand its role in the pathogenesis. EBV infection was screened by in situ hybridization for EBV-encoded non-polyadenylated RNA (EBER ISH) in 79 cases of gastric MALT lymphoma of nonimmunocompromised patients. The expression of EBV proteins [LMP1 (latent membrane protein 1), EBNA2 (EBV nuclear antigen 2), ZEBRA (switch protein encoded by BZLF1 gene)] was studied by immunohistochemistry in EBER-positive cases. EBV was detected with EBER ISH in 15 (19%) of the 79 cases. EBV was found in virtually all tumor cells in 2 cases of high-grade MALT lymphoma (2.5%) (EBV-associated), and was found only in occasional large or small lymphoid cells in 13 cases (16.5%). False positive EBER signal was detected in the mucinous glandular epithelial cells of gastric antrum with FITC-labeled oligonucleotide probe but not with digoxigenin or 35S-labeled riboprobes. Type II latency (EBER+LMP1+ EBNA2-) was detected in both EBV-associated cases. Type III latency (EBER+LMP1+EBNA2+) was also identified in one EBV-associated case besides latency II. Double labeling showed coexpression of LMP1 and EBNA2 in a small number of tumor cells, indicating the presence of type III latency in single cell level. In cases with only occasional EBER-positive large or small lymphoid cells, LMP1 and EBNA2 were not detected. ZEBRA was negative in all the cases. These findings suggest that EBV may contribute to the pathogenesis of a small proportion of high-grade MALT lymphoma, where virtually all tumor cells harbored EBV and the oncogenic viral protein LMP1 was expressed. Moreover, latency III of EBV infection may exist in nonimmunocompromised patient.

Regulation of PAK activation and the T cell cytoskeleton by the linker protein SLP-76

Tyrosine phosphorylation of linker proteins enables the T cell antigen receptor (TCR)-associated protein tyrosine kinases to phosphorylate and regulate effector molecules that generate second messengers. We demonstrate here that the SLP-76 linker protein interacts with both nck, an adaptor protein, and Vav, a guanine nucleotide exchange factor for Rho-family GTPases. The assembly of this tri-molecular complex permits the activated Rho-family GTPases to regulate target effectors that interact through nck. In turn, assembly of this complex mediates the enzymatic activation of the p21-activated protein kinase 1 and facilitates actin polymerization. Hence, phosphorylation of linker proteins not only bridges the TCR-associated PTK, ZAP-70, with downstream effector proteins, but also provides a scaffold to integrate distinct signaling complexes to regulate T cell function.

Progression of spontaneous lymphomas in SJL mice: monitoring in vivo clonal evolution with molecular markers in sequential splenic samples

SJL mice are an inbred strain with a high incidence of spontaneous lymphomas of the B-cell type. We used molecular markers of clonality to study the process of tumor progression of SJL lymphomas in vivo. This was accomplished at time intervals ranging from 2 to 116 days by initial partial splenectomy (biopsy) followed by spleen sampling at the time of killing (autopsy). Immunoglobulin heavy chain (IgH) gene rearrangement and murine leukemia virus (MuLV) proviral integration patterns were used to study the clonal identities of the sequential tumor pairs in 11 informative mice by Southern blot hybridization. Of these 11 mice, 5 showed the same number of IgH gene rearrangement bands in the matched biopsy-autopsy samples, indicating the persistence of the original lesions. In 2 of 11 mice, a decrease in the number of IgH gene rearrangement bands was seen, consistent with a process of clonal selection in the original oligoclonal population. Another 2 of 11 mice showed an increase in the IgH gene rearrangement bands, indicating the emergence of either a new unrelated clone or, less likely, a subclone with secondary IgH gene rearrangement. The remaining two mice showed differences between the patterns in biopsy and autopsy samples, as assessed by IgH gene rearrangement and the proviral integration analysis. This finding suggests that the biopsied tumor had regressed and new clones had emerged. Tumor development was also associated with an increase in the number of clonal MuLV insertions in all mice except one, in which no non-germline integration band was detected. Of 11 mice, 5 showed an increase in the extent of tumor involvement by microscopic examination of the biopsy and autopsy samples; 3 showed a decrease, whereas 2 showed no change. A change in tumor morphology toward a more dedifferentiated appearance was found in only 1 of 11 mice. Overall, the results did not show a single paradigm that tumor progression followed, rather they indicated a complex and dynamic process of clonal evolution, which is likely to be a major feature of lymphoma progression in vivo.

Vitamin E and atherosclerosis

Vitamin E was advocated as an effective treatment for heart disease by Dr. Even Shute of London, Ontario more than 50 years ago. His pioneering claims, which were unacceptable to the medical community at large, have been confirmed by recent findings from epidemiologic studies and clinical trials. This review integrates our current knowledge of atherogenesis with the biological functions of vitamin E. The response-to-injury hypothesis explains atherosclerosis as a chronic inflammatory response to injury of the endothelium, which leads to complex cellular and molecular interactions among cells derived from the endothelium, smooth muscle and several blood cell components. Inflammatory and other stimuli trigger an overproduction of free radicals, which promote peroxidation of lipids in LDL trapped in the subendothelial space. Products of LDL oxidation are bioactive, and they induce endothelial expression and secretion of cytokines, growth factors and several cell surface adhesion molecules. The last-mentioned are capable of recruiting circulating monocytes and T lymphocytes into the intima where monocytes are differentiated into macrophages, the precursor of foam cells. In response to the growth factors and cytokines, smooth muscle cells proliferate in the intima, resulting in the narrowing of the lumen. Oxidized LDL can also inhibit endothelial production of prostacyclin and nitric oxide, two potent autacoids that are vasodilators and inhibitors of platelet aggregation. Evidence is presented that vitamin E is protective against the development of atherosclerosis. Vitamin E enrichment has been shown to retard LDL oxidation, inhibit the proliferation of smooth muscle cells, inhibit platelet adhesion and aggregation, inhibit the expression and function of adhesion molecules, attenuate the synthesis of leukotrienes and potentiate the release of prostacyclin through up-regulating the expression of cytosolic phospholipase A2 and cyclooxygenase. Collectively, these biological functions of vitamin E may account for its protection against the development of atherosclerosis.

Detection of trisomy 3 in primary gastric B-cell lymphoma by using chromosome in situ hybridization on paraffin sections

Recent studies in Western populations have shown that trisomy 3 is the most frequent chromosomal abnormality in primary gastric lymphoma (PGL). To study the incidence of trisomy 3 and its implications for the pathogenesis of PGL in Hong Kong, we have applied the technique of chromosome in situ hybridization in 13 cases of PGL by using archival paraffin-embedded tissue sections. Five cases of chronic gastritis were used as controls. Trisomy 3 was found in 9 (69%) of 13 cases, including cases of low-grade lymphoma and high-grade lymphoma with or without a low-grade component. Our findings are similar to the incidence of trisomy 3 reported in the Western literature. The persistent finding of trisomy 3 in various histologic grades of PGL suggests that it may be useful as a clonal marker in this group of neoplasms. Various molecular events involving chromosome 3 may be related to the pathogenesis of this group of lymphomas.

Structural basis for Syk tyrosine kinase ubiquity in signal transduction pathways revealed by the crystal structure of its regulatory SH2 domains bound to a dually phosphorylated ITAM peptide

The Syk family of kinases, consisting of ZAP-70 and Syk, play essential roles in a variety of immune and non-immune cells. This family of kinases is characterized by the presence of two adjacent SH2 domains which mediate their localization to the membrane through receptor encoded tyrosine phosphorylated motifs. While these two kinases share many structural and functional features, the more ubiquitous nature of Syk has suggested that this kinase may accommodate a greater variety of motifs to mediate its function. We present the crystal structure of the tandem SH2 domain of Syk complexed with a dually phosphorylated ITAM peptide. The structure was solved by multiple isomorphous replacement at 3.0 A resolution. The asymmetric unit comprises six copies of the liganded protein, revealing a surprising flexibility in the relative orientation of the two SH2 domains. The C-terminal phosphotyrosine-binding site is very different from the equivalent region of ZAP-70, suggesting that in contrast to ZAP-70, the two SH2 domains of Syk can function as independent units. The conformational flexibility and structural independence of the SH2 modules of Syk likely provides the molecular basis for the more ubiquitous involvement of Syk in a variety of signal transduction pathways.

[Expression of cytotoxic-granule-associated protein TIA-1 in nasal NK/T cell lymphomas and lymphoid hyperplasia]

OBJECTIVE

27 cases of nasal NK/T cell lymphomas were studied for the expression of the cytotoxic-granule-associated protein TIA-1, its immunophenotype, genotype and Epstein-Barr virus infection status.

METHODS

Immunohistochemical staining for TIA-1, CD3, CD56, CD45RO, CD8, CD20; polymerase chain reaction (PCR) for TCR gamma chain gene and immunoglobulin JH chain gene rearrangement analysis; in situ hybridization for EBER 1/2 and double staining for TIA-1, CD8 with EBER 1/2. 10 cases of lymphoid hyperplasia were used for comparison.

RESULTS

(1) In the 27 cases of nasal NK/T cell lymphomas, most tumor cells expressed TIA-1, CD3, CD45RO and EBER 1/2; expression of CD56 was found in 26 cases; no CD8 or CD20 were detected in tumors cells of this series of cases. Double labelled staining showed that the TIA-1 positive tumor cells coexpress EBER 1/2. TCR gamma chain gene rearrangement was detected in only 1 of the 27 cases. (2) In the 10 cases of lymphoid hyperplasia of nasal pharynx, a small amount of TIA-1 positive cells were present in 8 cases and their distribution similar to that of CD8+ cells, in 4 of these cases a few EBER 1/2+ cells were detected, the number of CD45RO+ cells and CD20+ cells were similar in all 10 cases. Double labelled staining showed that the EBER 1/2+ cells did not coexpress TIA-1.

CONCLUSION

A high percentage of these tumor cells express TIA-1 and correlate with that of CD56, CD3 epsilon, CD45RO and EBER1/2 in nasal NK/T cell lymphomas. It is suggested that expression of TIA-1 in this tumor may be related to the tumor origin and may also be responsible for its special biologic behavior.

Isolated extramedullary relapse after allogeneic bone marrow transplantation for chronic myeloid leukemia

Relapse of chronic myeloid leukemia (CML) as extramedullary granulocytic sarcoma (GS) after allogeneic bone marrow transplantation (BMT) is a rare occurrence. We report two patients who developed spinal GS as the first indication of relapse after allogeneic BMT for CML. In both cases, the marrow was in morphologic and karyotypic remission. However, fluorescence in situ hybridization (FISH) successfully demonstrated the presence of a minor Ph-positive clone in the marrow, as well as an occult clone with an additional Ph chromosome detected in one case. The results indicated a stronger graft-versus-leukemia effect in the marrow than in the peripheral tissues.

BLNK: a central linker protein in B cell activation

Linker or adapter proteins provide mechanisms by which receptors can amplify and regulate downstream effector proteins. We describe here the identification of a novel B cell linker protein, termed BLNK, that interfaces the B cell receptor-associated Syk tyrosine kinase with PLCgamma, the Vav guanine nucleotide exchange factor, and the Grb2 and Nck adapter proteins. Tyrosine phosphorylation of BLNK by Syk provides docking sites for these SH2-containing effector molecules that, in turn, permits the phosphorylation and/or activation of their respective signaling pathways. Hence, BLNK represents a central linker protein that bridges the B cell receptor-associated kinases with a multitude of signaling pathways and may regulate the biologic outcomes of B cell function and development.

Primary CD30-positive anaplastic large cell lymphoma of the lip

We report a case of primary CD30-positive anaplastic large cell lymphoma of the lip. While extranodal involvement is not uncommon in Ki-1(CD30) anaplastic large cell lymphoma, this is the first reported case of primary lip involvement. The clinical features and clinical outcome in Ki-1 anaplastic large cell lymphoma are discussed.

Use of preoperative autologous blood donation in liver resections for colorectal metastases

BACKGROUND

Transfusion of allogeneic blood is associated with risks of human immunodeficiency virus and hepatitis transmission, transfusion reactions, and other potential immunologic and infectious complications. To determine if predonation of autologous blood impacts upon transfusion practice and clinical outcome following liver resection, clinical records of 379 consecutive patients undergoing hepatic resection for metastases of colorectal cancer were identified from the prospective hepatobiliary database and reviewed.

METHODS

Of the 379 hepatic resections performed for colorectal metastases between January 1991 and January 1996, 240 (63%) were hepatic lobectomy or trisegmentectomy. Thirty-two percent of patients (123 of 379) agreed to preoperative blood donation (POBD), and their clinical characteristics including age, preoperative hemoglobin, and operative mortality were comparable with those of patients without POBD. Liver resections were carried out using standard vascular inflow and outflow control. Parenchymal transections were performed bluntly with maintenance of low central venous pressure (0 to 5 cm H2O). No vascular isolation or normovolemic hemodilution was used intraoperatively. All erythrocyte transfusions during the entire hospital stay were considered and compared between the two groups.

RESULTS

Forty-five percent of patients (172 of 379) received blood transfusions during or after liver resections, of which 61% (105 of 172) required only 1 or 2 units. Only 17% of the POBD group required allogeneic blood. This was significantly less than the group without POBD (43%, P <0.01). There was no significant difference in the operative mortality (2.3% versus 4.9%, P = 0.2) and the median survival (50 versus 40 months, P = 0.3).

CONCLUSIONS

Major hepatic resections using current surgical techniques can be performed safely with low blood loss and transfusion is required for only a minority of patients. POBD further reduces transfusion requirement.

Randomized trial of early versus delayed laparoscopic cholecystectomy for acute cholecystitis

BACKGROUND

The aim of this prospective randomized study was to define the optimum management between early and delayed laparoscopic cholecystectomy for patients with acute cholecystitis.

METHODS

Patients were randomized to receive either early laparoscopic cholecystectomy within 24 h of randomization or initial conservative treatment followed by delayed laparoscopic cholecystectomy 6-8 weeks later.

RESULTS

There were 53 patients in the early group and 51 in the delayed group. There was no significant difference in conversion rate (early 21 per cent versus delayed 24 per cent), postoperative analgesic requirement (1 versus 2 doses) and postoperative complications. However, the early group had significantly longer operating time (122.8 versus 106.6 min, P = 0.04) and shorter total hospital stay (7.6 versus 11.6 days, P < 0.001).

CONCLUSION

Early laparoscopic cholecystectomy is safe and feasible for acute cholecystitis with the additional benefit of shorter total hospital stay. Apart from a shorter operating time, treating patients with delayed laparoscopic cholecystectomy does not offer additional benefit.

No evidence of replication error phenotype in primary gastric lymphoma of mucosa-associated lymphoid tissue

Replication error (RER) phenotype, caused by deficiency of DNA mismatch repair genes and revealed by widespread microsatellite instability, has been detected in subsets of a wide variety of solid tumors, but rarely in lymphomas in general. So far, the involvement of RER phenotype in the pathogenesis of gastric lymphoma of mucosa-associated lymphoid tissue (MALT) type has not been conclusively established. We therefore examined 9 microsatellite loci on 5 chromosomes [D2S123, D3S11, D3S1261, D3S1262, D3S1265, D6S262, D18S559, a CTTT(T) repeat in intron 20 of RBI gene and a CA repeat in p53 locus] in 33 cases of primary gastric MALT lymphoma for evidence of microsatellite instability by polymerase chain reaction using primers end-labeled with [gamma-33P] ATP. Although novel-length allele was observed in 7 of 33 cases (21.2%), none of these 7 cases showed changes in more than one locus. RER phenotype was scored as positive in a case when more than 1 of the 9 examined microsatellite loci showed length alterations. Accordingly, none of the 33 cases had a RER phenotype. This result suggests that the pathogenesis of gastric MALT lymphoma does not involve RER phenotype. It is consistent with the general observations in lymphomas, but is highly in contrast to a previous report showing more than 50% of MALT lymphomas with the RER phenotype.

Genetic evidence of a role for Lck in T-cell receptor function independent or downstream of ZAP-70/Syk protein tyrosine kinases

T-cell antigen receptor (TCR) engagement results in sequential activation of the Src protein tyrosine kinases (PTKs) Lck and Fyn and the Syk PTKs, ZAP-70 and Syk. While the Src PTKs mediate the phosphorylation of TCR-associated signaling subunits and the phosphorylation and activation of the Syk PTKs, the lack of a constitutively active Syk PTK has prohibited the analysis of Lck function downstream of these initiating signaling events. We describe here the generation of an activated Syk family PTK by substituting the kinase domain of Syk for the homologous region in ZAP-70 (designated as KS for kinase swap). Expression of the KS chimera resulted in its autophosphorylation, the phosphorylation of cellular proteins, the upregulation of T-cell activation markers, and the induction of interleukin-2 gene synthesis in a TCR-independent fashion. The KS chimera and downstream ZAP-70 or Syk substrates, such as SLP-76, were still phosphorylated when expressed in Lck-deficient JCaM1.6 T cells. However, expression of the KS chimera in JCaM1.6 cells failed to rescue downstream signaling events, demonstrating a functional role for Lck beyond the activation of the ZAP-70 and Syk PTKs. These results indicate that downstream TCR signaling pathways may be differentially regulated by ZAP-70 and Lck PTKs and provide a mechanism by which effector functions may be selectively activated in response to TCR stimulation.

Primary human herpes virus 6 infection transmitted from donor to recipient through bone marrow infusion

An 8.5-month-old boy with Wiskott-Aldrich syndrome received a sibling matched bone marrow transplant from his healthy non-identical twin brother. The donor had primary human herpes virus 6 (HHV-6) infection around the time of bone marrow donation. The recipient had hepatitis in the first week and then developed fever and rash on day 18. Skin biopsy was shown to have HHV-6 antigen and his peripheral blood leukocytes were HHV-6 DNA positive. He engrafted on day 18 but the ANC dropped from 5.5 x 10(9)/l (day 23) to 0.48 x 10(9)/l (day 34) with persistent HHV-6 DNAemia. Bone marrow on day 35 was positive for HHV-6 DNA. He was treated with G-CSF and ganciclovir with good response. He later had pneumonitis which was treated empirically with foscarnet, ceftazidime and clarithromycin.

Common bile duct stones become smaller after endoscopic biliary stenting

BACKGROUND AND STUDY AIMS

Endoscopic biliary stenting is often used for large or difficult common bile duct (CBD) stones that cannot be extracted at one session. We compared the sizes of the CBD stones after a period of stenting.

PATIENTS AND METHODS

Over a 6-year period, a total of 444 patients with large CBD stones (> 2 cm diameter) or difficult CBD stones were managed in our endoscopy unit, of which 46 were treated by endoscopic stenting. Twenty-eight had second ERCP for stone removal after a median period of 63 days (range 17-1002 days). The largest diameter of the stones and the CBD (after correction of magnification) before and after stenting were compared using the Wilcoxon signed test.

RESULTS

Before stenting the largest diameters of CBD stones were 11-46 mm (mean 24.9 mm) and decreased to 5-46 mm (mean 20.1 mm) after stenting. The difference in stone sizes was statistically significant although the CBD diameter pre- and post-stenting was not significantly different. The reduction in stone sizes was not significantly correlated with the duration of stenting.

CONCLUSION

CBD stones became smaller after stenting. As the difficulty of stone extraction increases with stone size, a period of stenting may make subsequent removal easier for patients with large or difficult CBD stones.

Frequent detection of Epstein-Barr virus-infected B cells in peripheral T-cell lymphomas

Although Epstein-Barr virus (EBV) positivity has been described in peripheral T-cell lymphomas (PTCLs) in Chinese patients, the cellular lineage of EBV-harbouring cells is unknown. Forty-four cases of PTCL were therefore studied by in situ hybridization (ISH) for EBV-encoded small non-polyadenylated RNA 1 and 2 (EBER), and the lineage of the EBER+ cells was determined by double labelling. The findings were further correlated with the clonality of EBV and the genotype of these EBER+ tumours. The results for the detection of EBV by ISH show that 23 of the 44 cases were EBER+. In 5/23 of the EBER+ cases, EBER was found in around 50 per cent of atypical cells and in 18/23 cases, EBER was found in a subpopulation of atypical cells. Among the EBER+ cases, all 15 tested showed clonal T-cell receptor gene rearrangement by Southern blot hybridization. Double labelling was successfully done in 11 EBER+ cases, and by comparison, EBER+/CD20+ B cells outnumbered the EBER+/CD3+ T cells in all these cases. EBV clonality analysis revealed that EBV was monoclonal in six EBER+ cases and biclonal in three cases. With the predominance of EBV+ B cells over EBV+ neoplastic T cells being observed in most of these cases, it is possible that the EBV-infected clonal population may be of B-cell lineage. This was supported in some cases where a faint clonal band was seen over a background smear in the gene rearrangement study of immunoglobulin heavy chain gene by polymerase chain reaction (PCR), indicating a minor B-cell clone. It is concluded that in EBV+ PTCL, EBV is preferentially localized in B cells rather than neoplastic T cells. The neoplastic T cells may support the clonal proliferation of a subpopulation of EBV+ B cells in PTCLs.

Mutation of the 5' noncoding region of the BCL-6 gene in low-grade gastric lymphoma of the mucosa-associated lymphoid tissue

BCL-6 gene rearrangement and hypermutations were investigated in four Hong Kong Chinese patients with low-grade gastric lymphoma of the mucosa-associated lymphoid tissue (MALToma). The former was studied by Southern analysis and the latter by the technique of polymerase chain reaction and denaturing gradient gel electrophoresis. BCL-6 gene rearrangement was not detectable in any of the four cases. However, mutations at both the E1.11 and E1.12 segments of the 5' noncoding region of the BCL-6 gene were found in two patients. This preliminary observation suggests that the mutations of the 5' noncoding region of the BCL-6 gene rather than gene rearrangement may be playing a more important role in the tumorigenesis of low-grade gastric MALToma. Further confirmation of this finding by studying a larger number of patients will be required.

Desmoplastic variant of ameloblastoma in Chinese patients

Desmoplastic ameloblastoma is a rare tumour, and we know of only 43 previously reported cases. We report seven Chinese patients (five men and two women) with the desmoplastic variant of ameloblastoma, which makes up 9% of all ameloblastomas diagnosed during the years 1981-1995. The age ranged from 18 to 68 years (mean 43). Five of the tumours were in the maxilla and two were in the mandible. Five of them were situated anteriorly, the remaining two cases involving both anterior and posterior maxilla. The features of the 42 cases previously reported were reviewed and were compared with those in the present study. Our results differ in that we found a male predominance, wider age range and more tumours in the maxilla. Histologically, this variant of ameloblastoma is characterized by abundant collagenous stroma. Because the epithelial clusters may show prominent squamous metaplasia or may be compressed into thin strands in most areas, the appearance may mimic a squamous odontogenic tumour or odontogenic fibroma. The behaviour of this variant of ameloblastoma is likely to be the same as that of the classic ameloblastoma.

Near tetraploidy in three cases of acute myeloid leukemia associated with mediastinal granulocytic sarcoma

Granulocytic sarcoma (GS) is a rare manifestation of acute myeloid leukemia (AML), blastic transformation of chronic myeloid leukemia, and the myelodysplastic syndromes. The mediastinum is an unusual site of presentation. We report a series of three female patients with mediastinal GS. They were characterized by the presence of large and bizarre blast cells and near tetraploidy on cytogenetic analysis. All three patients responded poorly to chemotherapy. Near tetraploid AML is a rare entity, usually present in male patients, and has not been associated with GS. The clinical and pathological similarities in these three cases suggest a distinct category of poor-risk AML for which more intensive treatment is needed.

Lysophosphatidylcholine stimulates the release of arachidonic acid in human endothelial cells

Lysophosphatidylcholine (lyso-PC) is a product of phosphatidylcholine hydrolysis by phospholipase A2 (PLA2) and is present in cell membranes, oxidized lipoproteins, and atherosclerotic tissues. It has the ability to alter endothelial functions and is regarded as a causal agent in atherogenesis. In this study, the modulation of arachidonate release by lyso-PC in human umbilical vein endothelial cells was examined. Incubation of endothelial cells with lyso-PC resulted in an enhanced release of arachidonate in a time- and concentration-dependent manner. Maximum arachidonate release was observed at 10 min of incubation with 50 microM lyso-PC. Lyso-PC species containing palmitoyl (C16:0) or stearoyl (C18:0) groups elicited the enhancement of arachidonate release, while other lysolipids such as lysophosphatidylethanolamine, lysophosphatidylserine, lysophosphatidylinositol, or lysophosphatidate were relatively ineffective. Lyso-PC-induced arachidonate release was decreased by treatment of cells with PLA2 inhibitors such as para-bromophenacyl bromide and arachidonoyl trifluoromethyl ketone. Furthermore, arachidonate release was attenuated in cells grown in the presence of antisense oligodeoxynucleotides that specifically bind cytosolic PLA2 mRNA. Treatment of cells with lyso-PC resulted in a translocation of PLA2 activity from the cytosolic to the membrane fractions of cells. Lyso-PC induced a rapid influx of Ca2+ from the medium into the cells, with a simultaneous enhancement of protein kinase C (PKC) activity in the membrane fractions. The lyso-PC-induced arachidonate release was attenuated when cells were preincubated with specific inhibitors of PKC (staurosporine and Ro31-8220) or a specific inhibitor of mitogen-activated protein kinase/extracellular regulated kinase kinase (PD098059). Taken together, the results of this study show that lyso-PC caused the elevation of cellular Ca2+ and the activation of PKC, which stimulated cytosolic PLA2 in an indirect manner and resulted in an enhanced release of arachidonate.