anti-tumor effect of AlkB homolog 3 knockdown in hormone- independent prostate cancer cells.

Castrate resistant prostate cancer (CRPC) is a disease that is resistant to both hormone therapy and chemotherapy. At present, no curative therapy for CRPC has been established. Therefore, it is necessary to determine a novel molecular target for the development of therapeutic agents. We previously reported that AlkB homolog 3 (ALKBH3) is highly expressed in prostate cancer but not in benign prostatic hyperplasia or in normal prostate epithelium and that the expression levels of ALKBH3 protein are significantly correlated with the hormone-independent state of prostate cancer. Moreover, ALKBH3 regulates the invasion of prostate cancer cells via the regulation of matrix metalloproteinase 9. Here, we show that ALKBH3 gene silencing markedly induces apoptosis in hormone-independent prostate cancer cell line DU145 but not in the normal prostate epithelial cell line PNT2. Moreover, the in vivo tumorigenicity of DU145 cells was significantly inhibited by the administration of ALKBH3 siRNA. Furthermore, the anchorage-independent growth of DU145 cells was inhibited by ALKBH3 knockdown and promoted by ALKBH3 overexpression, significantly. ALKBH3 shRNA-expressing prostate cancer cells formed significantly smaller tumors than those of control shRNA transfectants in an in vivo xenograft model. These findings suggest that ALKBH3 is a promising target molecule for the development of CRPC therapeutic agents.

Prognostic significance of CD45RO+ memory T cells in renal cell carcinoma.

BACKGROUND: Memory T cells are well known to have a critical role for host defense in humans. However, their role in actual human cancer remains largely unknown. In this study, we tried to reveal the clinical importance of tumour-infiltrating CD45RO+ memory T cells in renal cell carcinoma (RCC). METHODS: We analysed 105 patients with RCC, who received radical or partial nephrectomy. Those were 65 in TNM stage I, 7 in stage II, 15 in stage III, and 18 in stage IV, respectively. CD45RO expression was evaluated by immunohistochemistry. CD4 and CD8 expressions were also systematically assessed in the same manner. RESULTS: Patients with higher TNM stage or high nuclear grade were found to have higher densities of CD45RO. Furthermore, CD45RO status was positively correlated with preoperative C-reactive protein level. In prognostic analysis, CD45RO+lo patients had a significantly better prognosis than CD45RO+hi patients. There was also a significant difference between CD4+lo and CD4+hi groups, whereas no significant difference was observed in CD8 T-cell status. Finally, multivariate analysis revealed that CD45RO+ status was the independent prognostic factor for patient overall survival. CONCLUSION: CD45RO+ memory T-cell status has a significant independent prognostic value, indicating that the adaptive immune response is functionally critical in human RCC.

ALKBH3, a human AlkB homologue, contributes to cell survival in human non-small-cell lung cancer.

BACKGROUND: We have demonstrated for the first time that a novel human AlkB homologue, ALKBH3, contributes to prostate cancer development, but its clinical and biological roles in lung cancer remain unclear. METHODS: Expression of both mRNA and protein of PCA-1 was examined by RT-PCR and western blotting. We also assessed association with senescence and in vivo ALKBH3 treatment on orthotopic tumour cell inoculation, and analysed it clinicopathologically. RESULTS: We have since found novel biological roles for ALKBH3 in human lung cancers, particularly in adenocarcinoma. Our immunohistochemical analysis of human adenocarcinomas and squamous cell carcinomas of the lung not only showed overexpression of ALKBH3 in these tumours but the percentage of cells positive for ALKBH3 also correlated statistically to recurrence-free survival in adenocarcinoma. Knockdown of ALKBH3 by siRNA transfection induced expression of p21(WAF1/Cip1) and p27(Kip1) in the human lung adenocarcinoma cell line A549, resulting in cell cycle arrest, senescence and strong suppression of cell growth in vitro. In vivo, peritoneal tumour growth and dissemination was inhibited in nude mice, previously inoculated with the A549 cell line, by intraperitoneal injection of ALKBH3 siRNA + atelocollagen, as demonstrated by the reduction in both number and diameter of tumours developing in the peritoneum. CONCLUSION: We suggest that ALKBH3 contributes significantly to cancer cell survival and may be a therapeutic target for human adenocarcinoma of the lung.

Clinical importance of B7-H3 expression in human pancreatic cancer.

BACKGROUND: B7-H3 is a new member of the B7 ligand family and regulates T-cell responses in various conditions. However, the role of B7-H3 in tumour immunity is largely unknown. The purpose of this study was to evaluate the clinical significance of B7-H3 expression in human pancreatic cancer and the therapeutic potential for cancer immunotherapy. METHODS: We investigated B7-H3 expression in 59 patients with pancreatic cancer by immunohistochemistry and real-time PCR. Furthermore, we examined the anti-tumour effect of B7-H3-blocking monoclonal antibody in vivo in a murine pancreatic cancer model. RESULTS: Tumour-related B7-H3 expression was abundant in most human pancreatic cancer tissues and was significantly higher compared with that in non-cancer tissue or normal pancreas. Moreover, its expression was significantly more intense in cases with lymph node metastasis and advanced pathological stage. B7-H3 blockade promoted CD8(+) T-cell infiltration into the tumour and induced a substantial anti-tumour effect on murine pancreatic cancer. In addition, the combination of gemcitabine with B7-H3 blockade showed a synergistic anti-tumour effect without overt toxicity. CONCLUSION: Our data show for the first time that B7-H3 may have a critical role in pancreatic cancer and provide the rationale for developing a novel cancer immunotherapy against this fatal disease.

Effect of continuous morphine infusion on hypoxic-ischaemic brain damage of neonatal rats.

BACKGROUND: Opioids are commonly administered to critically ill neonates and infants for general anaesthesia and sedation. However, the clinical safety of these drugs, especially the effects on hypoxic-ischaemic damage of the developing brain, has not been well investigated. The present study was therefore conducted to investigate the effects of continuous morphine infusion on brain damage after hypoxic-ischaemic insults in neonatal rats. METHODS: Seven-day-old Sprague-Dawley rats were subjected to left common carotid artery ligation followed by a 90-min exposure of 8% oxygen. The rats were administered morphine (0.1, 0.3 or 1 mg/kg/h) or saline continuously for 72 h using osmotic minipumps. Seven days later, the rats were weighed and their brains were morphologically categorized into groups based on the following grades: 0=normal, 1=mild atrophy, 2=moderate atrophy, 3=atrophy with cystic cavitation <3 mm and 4=cystic cavitation >3 mm. For histological assessment, the ratio of the surviving neurons (ipsilateral/contralateral) was calculated in the cornu ammonis fields, CA1 and CA3, and the dentate gyrus (DG). RESULTS: One week after recovery (P14), the rats in the 1 mg/kg/h group showed significantly poorer weight gain compared with the other groups. However, the morphological score of the brains and the ratio of the surviving neurons in the CA1, CA3 and DG were similar among the groups. CONCLUSION: Our results indicate that continuous administration of morphine does not worsen brain damage 7 days after hypoxic-ischaemic insults in neonatal rats.

Impact of a left-lobe graft without modulation of portal flow in adult-to-adult living donor liver transplantation.

In adult-to-adult living donor liver transplantation (LDLT), left-lobe grafts can sometimes be small-for-size. Although attempts have been made to prevent graft overperfusion through modulation of portal inflow, the optimal portal venous circulation for a liver graft is still unclear. Hepatic hemodynamics were analyzed with reference to graft function and outcome in 19 consecutive adult-to-adult LDLTs using left-lobe grafts without modulation of graft portal inflow. Overall mean graft volume (GV) was 398 g, which was equivalent to 37.8% of the recipient standard liver volume (SV). The GV/SV ratio was less than 40% in 13 of the 19 recipients. Overall mean recipient portal vein flow (PVF) was much higher than the left PVF in the donors. The mean portal contribution to the graft was markedly increased to 89%. Average daily volume of ascites revealed a significant correlation with portal vein pressure, and not with PVF. When PVP exceeds 25 mmHg after transplantation, modulation of portal inflow might be required in order to improve the early postoperative outcome. Although the study population was small and contained several patients suffering from tumors or metabolic disease, all 19 patients made good progress and the 1-year graft and patient survival rate were 100%. A GV/SV ratio of less than 40% or PVF of more than 260 mL/min/100 g graft weight does not contraindicate transplantation, nor is it necessarily associated with a poor outcome. Left-lobe graft LDLT is still an important treatment option for adult patients.

The role of HRK gene in human cancer.

Apoptosis regulators play one of the most critical roles in tumorigenesis, and an imbalance between cell proliferation and apoptosis may contribute to tumor progression. HRK was itself originally identified as a proapoptotic gene induced by diminished levels of cytokine in hematopoietic cells and cultured neurons and repressed by the expression of death-repressor proteins. A few analyses of HRK protein expression in primary central nervous system lymphomas have been performed, and little is known about the epigenetic or post-transcriptional mechanisms that may participate in HRK inactivation. Here we show the data on the 5'-CpG methylation status, loss of heterozygosity on 12q13.1 and its association with HRK expression in human malignancies, including prostate cancers, astrocytic tumors and primary central nervous system lymphomas. Aberrant methylation of CpG islands within the promoter is an epigenetic event largely responsible for the silencing of the HRK gene and subsequent low apoptotic counts in our series of malignancies. Inactivation of HRK apparently occurs in a substantial proportion of all tumor phenotypes and, as a potential proapoptotic gene, HRK may contribute to the development and progression of many human cancers.

Prostatic volume and volume-adjusted prostate-specific antigen as predictive parameters for prostate cancer patients with intermediate PSA levels.

The object of the study was to examine the usefulness of volume-adjusted prostate-specific antigen (PSA) parameters for prediction of prostate cancer in the patients with intermediate PSA levels. The subjects were 235 patients with intermediate PSA levels (range: 4.1-10.0 ng/ml) whose prostate volume (PV) and prostate transition zone volume (TZV) were evaluated between August 1996 and April 2004. PSA, PV, TZV, PSA density (PSAD) (PSA/PV) and PSA transition zone density (PSATZD) (PSA/TZV) were assessed with the receiver operating characteristic (ROC) curve and the area under the curve (AUC). Simple and multivariate logistic regression analyses were used to analyze the odds ratios of age, PSA, PSAD, PSATZD, PV, TZV, digital rectal examination (DRE) and transrectal ultrasonography (TRUS) findings. Fifty-five patients (23.4%) of 235 patients had biopsy-proven prostate cancer. The univariate analysis revealed significant differences in the mean values of age, PSAD, PSATZD, PV, TZV and DRE between the patients with cancer and the non-cancer patients. The ROC curve analysis revealed that PV, TZV, PSAD and PSATZD had significant predictive values as compared with that of PSA. However, there was no difference in AUC between them. The stepwise logistic regression analysis showed that the age, PV, PSATZD and DRE had significant predictive values, and that PSATZD had the most predictive power. In conclusion, both PSAD and PSATZD had significant predictive values in discriminating prostate cancer. Furthermore, the stepwise logistic regression analysis showed that PSATZD had the strongest predictive value.

Genetic analysis to complement histopathological diagnosis of brain tumors.

Gliomas, the most frequent tumors originating in the human nervous system, are divided into various subtypes. Currently, microscopic examination alone is insufficient for classification and grading so that genetic profiles are increasingly being emphasized in recognition of the emerging role of molecular diagnostic approaches to glioma classification. Glioblastomas (WHO grade IV) may develop de novo (primary glioblastomas) or through progression from lower-grade astrocytomas (secondary glioblastomas), while both glioblastomas show similar histological features. In contrast, they do constitute distinct disease entities that evolve through different genetic pathways, and are likely to differ in prognosis and response to therapy. Oligodendrogliomas (WHO grade II) account for 2.7% of brain tumors and 5-18% of all gliomas. Since this tumor is recognized as a particular subtype of glioma that shows remarkable responses to chemotherapy, a correct diagnosis is of prime importance. The difficulty is that histological differentiation of oligodendrogliomas from diffuse astrocytomas is highly subjective in cases without typical morphological features and there is a lack of reliable immunohistochemical markers. While histological distinction of low-grade gliomas from reactive astrocytes is also often difficult, reactive astrocytes usually lack genetic alterations. More biological and molecular approaches to glioma classification thus appear warranted to provide improved means to achieve correct diagnoses.

FADD phosphorylation is critical for cell cycle regulation in breast cancer cells.

Anti-oestrogen therapy is effective for control of hormone receptor-positive breast cancers, although the detailed molecular mechanisms, including signal transduction, remain unclear. We demonstrated here that long-term tamoxifen treatment causes G2/M cell cycle arrest through c-jun N-terminal kinase (JNK) activation, which is dependent on phosphorylation of Fas-associated death domain-containing protein (FADD) at 194 serine in an oestrogen (ER) receptor-positive breast cancer cell line, MCF-7. Expression of a dominant negative mutant form of MKK7, a kinase upstream of JNK, or mutant FADD (S194A) in MCF-7 cells suppressed the cytotoxicity of long-term tamoxifen treatment. Of great interest, similar signallings could be evoked by paclitaxel, even in an ER-negative cell line, MDA-MB-231. In addition, immunohistochemical analysis using human breast cancer specimens showed a close correlation between phosphorylated JNK and FADD expression, both being significantly reduced in cases with metastatic potential. We conclude that JNK-mediated phosphorylation of FADD plays an important role in the negative regulation of cell growth and metastasis, independent of the ER status of a breast cancer, so that JNK/FADD signals might be promising targets for cancer therapy.

Molecular roles of MAP kinases and FADD phosphorylation in prostate cancer.

Mitogen activated protein (MAP) kinases are well known serine threonine kinases that modulate gene expression, mitosis, cell proliferation and programmed cell death or 'apoptosis' in response to various stresses. Extracellular stress regulated kinase (ERK), c-jun NH2 terminal kinase and p38 are major members of the MAP kinases, and there is now a body of evidence of their involvement in genesis or sensitivity to chemotherapy of human prostate cancers. In this review, we focus on the molecular roles of MAP kinases and their pathological correlations, with particular attention to novel downstream signals through phosphorylation of the Fas-associated death domain protein that effectively regulates not only apoptosis but also the cell cycle in prostate neoplastic cells.

Pentosidine and its deposition in renal tissue in renal transplantation.

BACKGROUND: Advanced glycation end products (AGEs) accumulate in lesions of arteriosclerosis, Alzheimer's disease, rheumatoid arthritis, diabetic retinopathy, and diabetic nephropathy. Among AGEs, chemical quantification and immunohistologic methods for pentosidine have been established. Free pentosidine-eliminated by renal excretion- is mainly affected by renal function. In this study, we measured concentrations of plasma free and total pentosidine and immunohistologically investigated kidney graft biopsy specimens in patients after renal transplantation to investigate the renal function, plasma free and total pentosidine, and its relationship with deposition in the renal tissue. PATIENTS AND METHODS: In 28 patients who underwent renal transplantation from 1996 to 2003, we measured the time course of plasma concentrations of free pentosidine, total pentosidine, and serum creatinine starting right after renal transplantation. Thirty-four graft biopsy specimens were immunohistologically investigated using anti-pentosidine antibody. Plasma free and total pentosidine, and serum creatinine were measured at the same time. RESULTS: Plasma free and total pentosidine were positively correlated with serum creatinine. Plasma free pentosidine and serum creatinine reached nadir values on day 34.2 +/- 14.2, when the blood concentrations were 5.1 +/- 1.6 pmol/mL and 1.7 +/- 0.7 mg/dL, respectively. Plasma total pentosidine reached a nadir on day 116.5 +/- 39.7 when the plasma concentration was 4.0 +/- 1.5 pmol/mg. We correlated the time required to reach the nadir of plasma free and total pentosidine concentrations. However, neither the concentration of plasma free nor plasma total pentosidine at nadir correlated with serum creatinine. The intensity of immunostaining with anti-pentosidine antibody in proximal tubular cells was graded as weakly positive, positive, or strongly positive. Significant differences were obtained among plasma free pentosidine values between the weakly positive and strongly positive groups. CONCLUSIONS: Renal transplantation improves renal function and decreases renal excretion of free pentosidine. Accordingly, total pentosidine also decreases. However, the concentrations of plasma free and total pentosidine at nadir varied among individuals; the blood concentrations were not determined by renal function alone. It was suggested that deposition of pentosidine in proximal tubular cells was more severe among patients with higher plasma free pentosidine and serum creatinine values.

PDX1 homeobox protein expression in pseudopyloric glands and gastric carcinomas.

BACKGROUND AND AIMS: Although it has been reported that intestinal metaplasia implicated in gastric carcinogenesis is induced by the ParaHox gene CDX2, it is unclear which genes are responsible for the formation of pseudopyloric glands and whether they play a role in gastric carcinogenesis. Pancreatic-duodenal homeobox 1 (PDX1) is also a ParaHox gene which contributes to the genesis and development of the pancreas, duodenum, and antrum. To clarify its significance for the formation of pseudopyloric glands and gastric carcinogenesis, we investigated expression of PDX1 and mucin in gastric carcinomas and surrounding mucosa. METHODS: Gastric carcinoma tissues from 95 patients were used for immunohistochemical analyses of PDX1, and mucins MUC6 and MUC5AC. RESULTS: PDX1 was found to be frequently expressed in pseudopyloric glands and intestinal metaplasia. MUC6 was more abundant than MUC5AC in pseudopyloric glands while higher levels of MUC5AC than MUC6 were evident in intestinal metaplasia. The frequency of PDX1 positive reactivity was higher in differentiated type carcinomas (39/43, 90.7%) and T1 carcinomas (42/43, 97.7%) than in undifferentiated type (33/52, 63.5%) and T2-4 (30/52, 57.7%) carcinomas. PDX1 and MUC6 double positive expression was observed in carcinomas, respectively, including the corpus, and also correlated with histological type and depth of invasion. In contrast, no link was apparent between PDX1 and MUC5AC double positive reactivity and histological type. CONCLUSION: Our study suggests that PDX1 plays an important role in the development of pseudopyloric glands, and that pseudopyloric glands may reflect a condition associated with gastric carcinogenesis.

Histopathology, pathogenesis and molecular genetics in primary central nervous system lymphomas.

Recent increases in the incidence of primary central nervous system lymphoma (PCNSL), a rare non-Hodgkin's lymphoma arising in the brain, have been noted in both immunodeficient and immunocompetent patients. Compared with lymphomas originating outside the central nervous system, the biology of PCNSL at the molecular or cytogenetic level has not been well characterized, yet it is important to thoroughly understand the etiology of this rare malignant lymphoma if effective therapies are to be developed. This review will focus on the epidemiology, clinical aspects, histopathology, pathogenesis, and molecular genetics of this aggressive, extranodal lymphoma in immunocompetent patients.

Androgen and the blocking of radiation-induced sensitization to Fas-mediated apoptosis through c-jun induction in prostate cancer cells.

PURPOSE: To clarify the key mechanism by which androgen makes prostate cancer cells highly resistant to Fas-mediated apoptosis. MATERIALS AND METHODS: The role of c-jun induction by 10 nM dihydrotestosterone (DHT) in 5 Gy radiation-induced up-regulation of Fas and sensitization to the apoptosis was studied by using the human prostate cancer cell line LNCaP. RESULTS: On exposure to 5 Gy radiation, LNCaP cells demonstrated high sensitization to Fas-mediated apoptosis through increased Fas expression, stabilized p53 expression and binding to p53 response elements within the promoter and first intronic region of the Fas gene. Following treatment with DHT, in vivo binding of p53 to its response elements was strongly inhibited. In addition, DHT significantly up-regulated c-jun expression through extracellular stress-regulated kinase (ERK) activation, and transfection of an antisense oligonucleotide for c-jun or ERK inhibition by PD98059 cancelled DHT-mediated suppression of radiation-induced transactivation of Fas gene and sensitization to Fas-mediated apoptosis. CONCLUSIONS: Radiation-induced Fas sensitization in prostate cancer cell was mediated through p53-dependent transactivation of the Fas gene, which can be blocked by androgen stimulation mainly through induction of c-jun.

Overexpression of leucocyte common antigen (LAR) P-subunit in thyroid carcinomas.

Protein tyrosine phosphatase (PTPase) dephosphorylation and protein tyrosine kinase (PTKs) phosphorylation of key signal transduction proteins may be regulated by extracellular signals, making PTPases important in the regulation of cell proliferation. Leucocyte common antigen (LAR), a receptor-like PTPase, consists of E-subunit, containing the cell adhesion molecule-like receptor region, and P-subunit specific for a short segment of the extracellular region, the transmembrane peptide, and two cytoplasmic PTPase domains. We produced a monoclonal antibody against the LAR P-subunit for immunohistochemical screening of LAR expression in normal and tumourous tissues. Gliomas and gastric, colorectal, lung, breast and prostate cancers showed weak and relatively infrequent expression. Intense and diffuse expression, however, was detected in 95% (227 out of 239) of thyroid carcinomas, but only 12% (22 out of 128) of adenomas and no cases of benign thyroid disease were immunopositive. In contrast to broad staining in carcinomas, LAR expression in thyroid adenomas was often found in small focal or locally invasive areas. Western blot analysis similarly detected LAR P-subunit protein in thyroid carcinomas, but not in normal tissues. We believe this to be the first demonstration of LAR overexpression in thyroid carcinoma and may help to elucidate the role of PTPases in the development of malignancy.

Aberrations of the p14(ARF) and p16(INK4a) genes in renal cell carcinomas.

The INK4a / ARF locus on chromosome 9p21, which encodes two distinct genes, p14(ARF) and p16(INK4a), is frequently altered in human neoplasms. To investigate the potential roles of p14(ARF) and p16(INK4a) genes in human renal cell carcinomas (RCCs), we analyzed 6 human RCC cell lines and 91 primary RCCs for homozygous deletion, promoter hypermethylation and expression of the p14(ARF) and p16(INK4a) gene products using differential PCR, methylation-specific PCR, and immunohistochemistry, respectively. Five cell lines showed homozygous co-deletion of both genes and one demonstrated promoter hypermethylation of the p16(INK4a) gene only. Eight of 91 RCCs showed aberrations of p14(ARF) or p16(INK4a) status and six of these featured gross extension into the renal vein. The results suggest that p14(ARF) and p16(INK4a) aberrations may play roles in the relatively late stage of renal tumorigenesis associated with tumor progression.

FR167653, a potent suppressant of interleukin-1 and tumor necrosis factor-alpha production, ameliorates colonic lesions in experimentally induced acute colitis.

BACKGROUND: Interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) are believed to play a significant role in the pathogenesis of inflammatory bowel disease (IBD). Interleukin-1 and TNF-alpha possess overlapping and synergetic activities inducing the production in cascade of other cytokines, adhesion molecules, arachidonic acid metabolites, as well as activating immune and non-immune cells. FR167653 (C24H18FN5O2-H2SO4-H2O) is a newly synthesized organic compound with a potent inhibitory effect on IL-1beta and TNF-alpha production. We hypothesized that the suppression of IL-1 and TNF-alpha induced by FR167653 could effectively attenuate experimentally induced colonic damage. METHODS: Colonic lesions were induced in male Sprague-Dawley rats (250-300 g) by intrarectal instillation of 4% acetic acid. The effect of FR167653 administration at 1.0, 1.5, 2.5 mg/kg per 6 h subcutaneously on acetic acid-induced colonic damage was assessed. The lesion area, microscopic findings, colonic and serum levels of TNF-alpha and IL-1beta were also evaluated. RESULTS: Treatment with FR167653 at 1.5 and 2.5 mg/kg per 6 h was able to ameliorate the gross macroscopic appearance of colonic lesions significantly, as well as ameliorate the lesion area induced by acetic acid. Colonic mucosal TNF-alpha and IL-1beta levels of rats treated with FR167653 showed significant decrease in a dose-dependent fashion compared with the control group. In the same manner, serum TNF-alpha of rats treated with FR167653 was significantly lower than that of respective controls. CONCLUSIONS: Subcutaneous administration of FR167653 was able to ameliorate the acute changes induced by acetic acid instillation in a dose-dependent manner. This is the first report to evaluate the dual inhibition of the production of IL-1 and TNF-alpha, offered by FR167653, in acute experimental colitis. Further studies are necessary to evaluate FR167653's efficacy and safety on long-term conditions.

Frequent alterations of the p14(ARF) and p16(INK4a) genes in primary central nervous system lymphomas.

To elucidate the role of p53/p16(INK4a)/RB1 pathways in the tumorigenesis of primary central nervous system lymphomas (PCNSLs), we have analyzed p14(ARF), p16(INK4a), RB1, p21(Waf1), and p27(Kip1) status in a series of their 18 sporadic cases of diffuse large B-cell lymphoma, using methylation-specific PCR, differential PCR, and immunohistochemistry. Homozygous deletion or methylation of p14(ARF) was detected in 10 (56%) PCNSLs, and they were almost entirely deletions (except 1 case). A total of 11 (61%) PCNSLs demonstrated homozygous deletion (6 cases) or methylation (5 cases) of p16(INK4a). Six tumors showed both p14(ARF) and p16(INK4a) homozygous deletions. Hypermethylation of the RB1 and the p27(Kip1) promoter region was detected in 2 (11%) cases, whereas p21(Waf1) methylation was not detected in any. Immunohistochemistry revealed loss of p14(ARF) and p16(INK4a) expression in 10 (56%) samples, correlating with the gene status. Four cases showed independent negative immunoreactivity for pRB and p27(Kip1), and nearly one-half of cases (8 of 18; 44%) were characterized by lack of p21(Waf1) expression. These results indicate that inactivation of p14(ARF) and p16(INK4a) by either homozygous deletion or promoter hypermethylation represents an important molecular pathogenesis in PCNSLs. Hypermethylation of RB1, p21(Waf1), and p27(Kip1) appears to be of minor significance, these genes being independently methylated in PCNSLs.