Jong Sun Choi

Primary central nervous system lymphoma in Korea: comparison of B- and T-cell lymphomas.

The great majority of primary central nervous system lymphoma (PCNSL) is known to be of B-lineage, with T-cell PCNSL (T-PCNSL) accounting for <5%. We report an unusually high incidence of T-cell lymphoma among the PCNSLs originated in a large general-care hospital in the metropolitan Seoul area. PCNSLs (n = 42) accrued from April 1995 through June 2001 were reviewed for histologic and clinical features, and immunohistochemical staining was done for CD3, CD20, CD4, CD8, Bcl-6, and CD10. Clonal rearrangements of the TCR-&ggr; and IgH genes were studied with semi-nested PCR in all seven cases of T-PCNSL and seven of 35 B-cell PCNSL (B-PCNSL). Formalin-fixed, paraffin-embedded specimens were used in all these studies. By immunohistochemical staining and molecular studies, seven cases (16.7%) were diagnosed as T-PCNSL, each displaying clonal rearrangement of the TCR-&ggr; gene, and 35 (83.3%) as B-PCNSL. Radiologically, T-PCNSL was significantly correlated with the superficial and subcortical lobar location (p <0.001), solitary mass formation (p = 0.001), presence of rim enhancement (p <0.001), and peritumoral edema (p = 0.029). Involvement of cerebrospinal fluid was observed only in B-PCNSL (n = 17) but not in T-PCNSL (p = 0.010). Histologically, T-PCNSL was characterized by a population of mixed predominantly small- and occasionally medium-sized cells (p <0.001), which were loosely scattered without forming a solid mass (p = 0.024), and perivascular infiltration was frequent (p = 0.007), in contrast to predominantly large cells of B-PCNSL, i.e., diffuse large B-cell lymphoma (DLBCL), in which the cells tended to aggregate to form monomorphous sheets (p = 0.024). In T-PCNSL, staining for CD8 was positive in five, including one with coexpression of CD4, and two were negative for CD4 and CD8. Of 24 DLBCLs tested, the pattern of Bcl-6+ tumor cells was diffusely dense, similar to that of the germinal center in nine cases (37.5%), with coexpression of CD10 in three of the nine cases. T-PCNSL accounted for 16.7% of the PCNSLs; thus, in Korea it may not be as rare as previously known. The T-PCNSL presented with certain clinical and pathologic features that were distinct from B-PCNSL and displayed preponderance of CD8 expression. DLBCL of the germinal center B-cell derivation defined by bcl-6 expression comprised 37.5% of DLBCL of the brain.

MET Expression in Sporadic Renal Cell Carcinomas

Although germline mutations of met proto-oncogene on human chromosome 7q31-34 have been known as useful molecular markers of hereditary papillary renal cell carcinoma (RCC), the expression of MET, a product of met proto-oncogene, has not been fully studied in sporadic RCC, along with its clinical significance. We investigated the expression of MET by immunohistochemistry in 182 cases of renal neoplasm encompassing 145 RCC, 25 urothelial carcinomas of renal pelvis, and 12 oncocytomas. MET was diffusely and strongly expressed in 90% of papillary RCC, all collecting duct carcinomas, and 92% of urothelial carcinomas of renal pelvis. On the contrary, clear cell RCC, chromophobe RCC, and oncocytomas were negative or focally positive for MET expression. In clear cell RCC, MET expression was positively correlated with high nuclear grade, presence of infiltrative growth, tumoral necrosis, papillary architecture, sarcomatoid component, tumoral involvement of the renal pelvis or ureter, involvement of the calyx, and lymphatic invasion. In conclusion, diffuse and strong expression of MET in papillary RCC and collecting duct carcinoma might be helpful in discriminating from the other subtypes of RCC with tubular or papillary growth. In case of MET expression observed in clear cell RCC, it might correlate with those clinicopathological parameters implying aggressive behavior.

Overexpression of CD24: association with invasiveness in urothelial carcinoma of the bladder.

CONTEXT CD24, originally described as a B-cell marker, has gained considerable attention in tumor research. High rates of CD24 expression have been found in several types of carcinomas that are significantly associated with a more aggressive course of the disease. To our knowledge, the expression of CD24 in urothelial carcinoma (UC) of the bladder has not been previously reported. OBJECTIVE To determine the expression of CD24 in UCs and the association between CD24 levels and tumor grade and stage. DESIGN Urothelial carcinomas (48 cystectomy, 87 transurethral biopsy), including 56 pTa, 29 pT1, 19 pT2, and 31 pT3, were analyzed immunohistochemically using an anti-CD24 monoclonal antibody. The intensity of CD24 staining was semiquantitatively scored as high-level or low-level expression. RESULTS In normal urothelium, CD24 was localized to the cytoplasm of the luminal cell layer with very low intensity. CD24 expression was upregulated in noninvasive UCs, and a high level of expression was correlated with the tumor grade (P = .003). Invasive UCs demonstrated strong diffuse cytoplasmic overexpression of CD24 and the difference in CD24 expression between invasive and noninvasive UC was statistically significant (P < .001). CONCLUSIONS CD24 protein is overexpressed in a significant number of bladder UCs. The high level of CD24 expression with loss of apical localization is a marker for stromal invasion and high tumor grade in UC. This study provides the basis for future investigations of CD24 as a potential serum marker or target of antibody-based therapeutics in bladder UC.

Critical evaluation of Bcl-6 protein expression in diffuse large B-cell lymphoma of the stomach and small intestine.

Diffuse large B-cell lymphoma (DLBCL) of the gastrointestinal tract is heterogeneous, including mucosa-associated lymphoid tissue (MALT) origin and non-MALT, and they are indistinguishable. MALT lymphoma is a tumor of a post-germinal center (GC) memory B-cell origin, which is negative for Bcl-6 protein expression in low-grade but may become positive in high-grade tumors. Because Bcl-6 expression patterns in lymphoma of GC and non-GC B-cell origins have recently been characterized and CD10 is generally regarded as a specific marker for GC B cells, we critically evaluated gastric and small intestinal DLBCLs to see whether it is possible to identify tumor of GC B-cell origin by immunostaining in archival specimens. High-grade MALT lymphoma (H-ML) of the stomach (n = 20) was defined by the presence of a concomitant lymphoepithelial lesion and/or follicular colonization; and DLBCLs de novo, both gastric (n = 31) and intestinal (n = 21), were defined by the absence of the above features. Immunostaining for Bcl-6 and CD10 was done using formalin-fixed, paraffin-embedded sections and was examined independently by three pathologists. Staining for Bcl-6 was positive (>10% of tumor cells) in 55 of 72 cases. However, two distinct patterns were recognized among those positive: diffusely dense (>75%) and sporadic (<75%). The former was further characterized by a consistency of Bcl-6+ tumor cell density at any given area, resembling the staining pattern of the GC or follicular lymphoma (FL) (GC/FL pattern), whereas the latter was, besides less dense population, by variable density from area to area. The GC/FL pattern was observed in 36% and 38% of gastric and intestinal DLBCLs de novo, respectively, but in none of the gastric H-ML. CD10 was positive in 12 of 71 cases (17%), all coexpressing Bcl-6. CD10+ tumors were more frequent in the intestinal (33%) than in gastric DLBCLs (∼15%). Significantly, CD10 expression was observed in three gastric H-MLs, including one that displayed a distinct lymphoepithelial lesion. In conclusion: 1) tumors showing a diffusely dense pattern of Bcl-6 expression should be distinguished from those showing a sporadic pattern; for the former most likely represents the tumor of GC B-cell derivation, and the latter non-GC, including MALT lymphoma; 2) tumor of GC B-cell origin thus defined accounted for about one third of gastric as well as intestinal DLBCLs de novo but none of the gastric H-ML; and 3) CD10 expression can be seen in MALT lymphomas and should not be used as the marker for GC B cells.

Effects of gate electrode work function on electrical characteristics of pentacene-based field-effect devices

This paper presents the effects of the work function of an indium tin oxide (ITO) gate electrode on the electrical characteristics of two pentacene-based field-effect devices—metal-insulator-semiconductor (MIS) capacitors and field-effect transistors (FETs). The ITO work function was varied by employing base and acid treatments. Flat-band voltage shifts of the MIS capacitors were found to result from the shift in the work function. The current onset and threshold voltage of the FETs were also found to be influenced by the work function. These results demonstrate the correlation of the flat-band conditions of pentacene-based field-effect devices with the gate electrode work function.

Effects of Interfacial Charge Depletion in Organic Thin-Film Transistors with Polymeric Dielectrics on Electrical Stability

We investigated the electrical stabilities of two types of pentacene-based organic thin-film transistors (OTFTs) with two different polymeric dielectrics: polystyrene (PS) and poly(4-vinyl phenol) (PVP), in terms of the interfacial charge depletion. Under a short-term bias stress condition, the OTFT with the PVP layer showed a substantial increase in the drain current and a positive shift of the threshold voltage, while the PS layer case exhibited no change. Furthermore, a significant increase in the off-state current was observed in the OTFT with the PVP layer which has a hydroxyl group. In the presence of the interfacial hydroxyl group in PVP, the holes are not fully depleted during repetitive operation of the OTFT with the PVP layer and a large positive gate voltage in the off-state regime is needed to effectively refresh the electrical characteristics. It is suggested that the depletion-limited holes at the interface, i.e., interfacial charge depletion, between the PVP layer and the pentacene layer play a critical role on the electrical stability during operation of the OTFT.

FABRICATION OF ORGANIC THIN-FILM TRANSISTORS BASED ON HIGH DIELECTRIC NANOCOMPOSITE INSULATORS

Organic thin-film-transistors (OTFTs) with solution-processed high dielectric gate insulators were fabricated. The gate insulators were made of high dielectric TiO2 nanoparticles dispersed uniformly in a polymer matrix of nylon 6 which is known to align liquid crystal molecules. It was found that the nanocomposite insulator in a pentacene-based OTFT reduces the operating voltage but it produces substantial current leakage. A buffer layer of polyvinylphenol on the top of the nanocomposite layer was found to block the leakage current and to increase significantly the carrier mobility as well as the current on-off ratio.

Admittance Spectroscopic Characteristics and Equivalent Circuit Modeling of Small Molecule-Based Organic Light Emitting Diodes

Admittance or impedance spectroscopy is one of the powerful tools to study the equivalent circuit models and the dielectric relaxation processes in organic and inorganic materials and devices. The frequency-dependent properties of small molecule-based organic light emitting diodes have been studied. The single-layer diodes can be modeled as a simple parallel resistor–capacitor circuit. The equivalent circuit models of double-layer devices, for which the single-layer device model is expanded and the interface properties between the organic layers are included, are suggested.

Pentacene TFT With Reduced Threshold Voltage Using PMMA-co-MAA/Sol-Gel-Derived

We report improvements in the characteristics of pentacene thin-film transistors (TFTs) achieved by using a poly(methylmethacrylate-co-methacrylic acid) (PMMA-co-MAA)/sol-gel-derived TiO2 composite insulator. The gate-leakage current of TFTs containing this insulator is comparable to that of devices composed of bare PMMA-co-MAA. The reduction in the threshold voltage is the most pronounced improvement observed herein (compared to the variations of other characteristic parameters). This can be explained by the negative surface potential of the sol-gel-derived TiO2 film.

\hbox{TiO}_{2}

Composite materials of poly(4-vinylphenol) (PVP) and titanium dioxide (TiO2) nanoparticles were fabricated via a spin coating process in order to enhance dielectric properties for a gate insulator application of the OTFT in this study. In order to improve dispersion stability of the TiO2 nanoparticles in the polymeric solution during the process, a surfactant was also adopted onto the solution mixture. The dispersion property was observed by measuring sedimentation time of TiO2 particles in the polymeric solution, and the effect of surfactant on the surface morphology of the dielectric layer was further analyzed by using atomic force microscopy. Dielectric properties of the PVP-TiO2 composite and performance of OTFTs with the PVP-TiO2 composite insulator are presented, along with their effects on device performance with pentacene layer as a semiconductor.