Bcl-2 family proteins and the regulation of programmed cell death in leukemia and lymphoma

High-Throughput Drug Screen for Potential Combinations With Venetoclax Guides the Treatment of Transformed Follicular Lymphoma

Transformed follicular lymphoma (t-FL) is an aggressive malignancy that is refractory and rapidly progressing with poor prognosis. There is currently no effective treatment. High-throughput screening (HTS) platforms are used to profile the sensitivity or toxicity of hundreds of drug molecules, and this approach is applied to identify potential effective treatments for t-FL. We randomly selected a compound panel from the School of Pharmaceutical Sciences Xiamen University, tested the effects of the panel on the activity of t-FL cell lines using HTS and the CCK-8 assay, and identified compounds showing synergistic anti-proliferative activity with the Bcl-2 inhibitor venetoclax (ABT-199). Bioinformatics tools were used to analyze the potential synergistic mechanisms. The single-concentration compound library demonstrated varying degrees of activity across the t-FL cell lines evaluated, of which the Karpas422 cells were the most sensitive, but it was the cell line with the least synergy with ABT-199. We computationally identified 30 drugs with synergistic effects in all cell lines. Molecularly, we found that the targets of these 30 drugs didn't directly regulate Bcl-2 and identified 13 medications with high evidence value above .9 of coordination with ABT-199, further confirming TP53 may play the largest role in the synergistic effect. Collectively, these findings identified the combined regimens of ABT-199 and further suggested that the mechanism is far from directly targeting Bcl-2, but rather through the regulation and synergistic action of p53 and Bcl-2. This study intended to reveal the best synergistic scheme of ABT-199 through HTS to more quickly inform the treatment of t-FL.

Role of Non-Coding RNAs in the Development of Targeted Therapy and Immunotherapy Approaches for Chronic Lymphocytic Leukemia

In the past decade, novel targeted therapy approaches, such as BTK inhibitors and Bcl2 blockers, and innovative treatments that regulate the immune response against cancer cells, such as monoclonal antibodies, CAR-T cell therapy, and immunomodulatory molecules, have been established to provide support for the treatment of patients. However, drug resistance development and relapse are still major challenges in CLL treatment. Several studies revealed that non-coding RNAs have a main role in the development and progression of CLL. Specifically, microRNAs (miRs) and tRNA-derived small-RNAs (tsRNAs) were shown to be outstanding biomarkers that can be used to diagnose and monitor the disease and to possibly anticipate drug resistance and relapse, thus supporting physicians in the selection of treatment regimens tailored to the patient needs. In this review, we will summarize the most recent discoveries in the field of targeted therapy and immunotherapy for CLL and discuss the role of ncRNAs in the development of novel drugs and combination regimens for CLL patients.

Expression of Beclin 1 and Bcl-2 in pancreatic neoplasms and its effect on pancreatic ductal adenocarcinoma prognosis

Aberrant expression of Beclin 1 and B-cell lymphoma-2 (Bcl-2) has been identified in a variety of human tumors; however, little information is available for pancreatic neoplasms. The present study analyzed the expression of Beclin 1 and Bcl-2 in pancreatic ductal adenocarcinoma (PDAC) and solid pseudopapillary neoplasm (SPN) of the pancreas, and evaluated their prognostic significance for PDAC. The present study included 117 PDAC, 43 SPN and 32 chronic pancreatitis (CP) cases. Levels of Beclin 1 and Bcl-2 expression were evaluated semiquantitatively by immunohistochemistry, and their correlation with the survival of patients with PDAC was determined. Beclin 1 was upregulated in 74 (63.2%) PDAC, 26 (60.5%) SPN, and 14 (43.8%) CP cases. Bcl-2 was upregulated in 38 (32.5%) PDAC, 11 (25.6%) SPN and 24 (75.0%) CP cases. High Beclin 1 and low Bcl-2 expression was significantly correlated with poor differentiation and distant metastasis in PDAC, and associated with the presence of nuclear pleomorphism in SPN and with advanced Tumor-Node-Metastasis stage in PDAC. Beclin 1 and Bcl-2 levels were inversely correlated in PDAC, whereas they were positively correlated in SPN. Low Beclin 1 and high Bcl-2 expression was associated with improved disease-free survival and overall survival (OS). However, the association of Beclin 1 with survival was not significant in the Cox analysis, whereas Bcl-2 expression was significantly correlated with OS in the multivariate analysis. In conclusion, Beclin 1 upregulation exacerbated the progression and aggressiveness of pancreatic neoplasms, and Bcl-2 downregulated expression was an independently poor prognostic factor for PDAC.

Hematologic malignancies: newer strategies to counter the BCL-2 protein

INTRODUCTION

BCL-2 is the founding member of the BCL-2 family of apoptosis regulatory proteins that either induce (pro-apoptotic) or inhibit (anti-apoptotic) apoptosis. The anti-apoptotic BCL-2 is classified as an oncogene, as damage to the BCL-2 gene has been shown to cause a number of cancers, including lymphoma. Ongoing research has demonstrated that disruption of BCL-2 leads to cell death. BCL-2 is also known to be involved in the development of resistance to chemotherapeutic agents, further underscoring the importance of targeting the BCL-2 gene in cancer therapeutics. Thus, numerous approaches have been developed to block or modulate the production of BCL-2 at the RNA level using antisense oligonucleotides or at the protein level with BCL-2 inhibitors, such as the novel ABT737.

METHODS

In this article, we briefly review previous strategies to target the BCL-2 gene and focus on a new approach to silence DNA, DNA interference (DNAi).

RESULTS AND CONCLUSION

DNA interference is aimed at blocking BCL-2 gene transcription. Evaluations of this technology in preclinical and early clinical studies are very encouraging and strongly support further development of DNAi as cancer therapeutics. A pilot phase II clinical trial in patients with relapsed or refractory non-Hodgkin lymphoma, PNT2258 demonstrated clinical benefit in 11 of 13 patients with notable responses in diffuse large B cell lymphoma and follicular lymphoma. By targeting the DNA directly, the DNAi technology promises to be more effective compared with other gene-interference strategies that target the RNA or protein but leaves the dysregulated DNA functional.

Investigation of Astragalus honey and propolis extract's cytotoxic effect on two human cancer cell lines and their oncogen and proapoptotic gene expression profiles

Background:

Cancer is one of the major fatal human diseases. Natural products have been used in the treatment of cancer for long time. Bee products including honey and propolis have been introduced for malignancy treatment in recent decades. In this study cytotoxicity of bee products and their effects on the expression of proapoptotic genes have been investigated.

Materials and Methods:

Cytotoxic effects of Astragalus honey, ethanol extract of propolis and a sugar solution (as control) against HepG2, 5637 and L929 cell lines have been evaluated by the MTT assay. Total RNAs of treated cells were isolated and p53 and Bcl-2 gene expression were evaluated, using real-time PCR.

Results:

Propolis IC50 values were 58, 30 and 15 μg/ml against L929, HepG2 and 5637, respectively. These values for honey were 3.1%, 2.4% and 1.9%, respectively. Propolis extract has increased the expression of the Bcl-2 gene in all cell lines whereas the honey decreased that significantly (P < 0.05). Also, we found that honey and propolis decreased p53 gene expression in HepG2 and 5637 significantly but not in L929 cells. The sugar solution increased the expression of p53 in two cancer cell lines but no significant changes were observed in the expression of this gene in L929 as normal mouse cell.

Conclusion:

By downregulation of Bcl-2 expression it could be concluded that the cytotoxicity of honey was more than two fold against tested cancer cells compared with the sugar solution. No significant changes were observed in the expression of p53 in honey-treated cells. Propolis had no significant effect on Bcl-2 and p53 gene expressions (P > 0.05).

Gene expression profiling of non-hodgkin lymphomas

BACKGROUND

Chromosomal translocations are genetic aberrations associated with specific non-Hodgkin lymphoma (NHL) subtypes. This study investigated the differential gene expression profile of Egyptian NHL cases based on a microarray approach.

MATERIALS AND METHODS

The study included tissue samples from 40 NHL patients and 20 normal lymph nodes used as controls. Total RNA was extracted and used for cDNA microarray assays. The quantitative real time polymerase chain reaction was used to identify the aberrantly expressed genes in cancer.

RESULTS

Significant associations of 8 up-regulated and 4 down-regulated genes with NHL were observed. Aberrant expression of a new group of genes not reported previously was apparent, including down-regulated NAG14 protein, 3 beta hydroxy-delta 5-c27 steroid oxi-reductase, oxi-glutarate dehydrogenase (lipo-amide), immunoglobulin lambda like polypeptide 3, protein kinase x linked, Hmt1, and caveolin 2 Tetra protein. The up-regulated genes were Rb binding protein 5, DKFZP586J1624 protein, protein kinase inhibitor gamma, zinc finger protein 3, choline ethanolamine phospho-transferase CEPT1, protein phosphatase, and histone deacetylase-3.

CONCLUSIONS

This study revealed that new differentially expressed genes that may be markers for NHL patients and individuals who are at high risk for cancer development.

A novel Cdk9 inhibitor preferentially targets tumor cells and synergizes with fludarabine

Cdk9 is a key elongation factor for RNA transcription and functions by phosphorylating the C-terminal domain of RNA polymerase II. Here we present direct evidence that cdk9 is important for cancer cell survival and describe the characterization of the potent cdk9 inhibitor CDKI-73 in primary human leukemia cells. CDKI-73 induced caspase-dependent apoptosis that was preceded by dephosphorylation of cdk9 and serine 2 of RNA polymerase II. CDKI-73 was more potent than the pan-cdk inhibitor flavopiridol and showed >200-fold selectivity against primary leukemia cells when compared with normal CD34+ cells. Furthermore, CDKI-73 was equipotent in poor prognostic sub-groups of leukemia patients and showed cytotoxic synergy with the nucleoside analog fludarabine. The Mechanism of synergy was associated with CDKI-73-mediated transcriptional inhibition of MCL1 and XIAP that was maintained when used in combination with fludarabine. Our data present a strong rationale for the development of cdk9 inhibitors such as CDKI-73 as anticancer therapeutics.

Ethyl 2-amino-6-(3,5-dimethoxyphenyl)-4-(2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate (CXL017): a novel scaffold that resensitizes multidrug resistant leukemia cells to chemotherapy

Multidrug resistance (MDR) is a major hurdle in the treatment of cancer, and there is a pressing need for new therapies. We have recently developed ethyl 2-amino-6-(3,5-dimethoxyphenyl)-4-(2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate (CXL017), derived from a dual inhibitor of Bcl-2 and SERCA proteins, sHA 14-1, with selective cytotoxicity toward MDR cancer cell lines in vitro. In this study, we present new evidence for its therapeutic potential in treatment of MDR cancers and offer mechanistic insights toward its preferential targeting of drug-resistant cancer. CXL017 selectively suppressed the growth of tumors derived from the MDR cancer cell line, HL60/MX2, in vivo. In addition, even after chronic exposure to CXL017, HL60/MX2 failed to develop stable resistance to CXL017, whereas it acquired >2000-fold resistance to cytarabine (Ara-C), the major first-line chemotherapy for the treatment of acute myeloid leukemia (AML). Remarkably, instead of acquiring further cross-resistance, HL60/MX2 cells exposed to CXL017 were resensitized to standard therapies (10- to 100-fold). Western blotting analyses revealed that CXL017 exposure significantly down-regulated Mcl-1 and Bax and up-regulated Noxa, Bim, Bcl-X(L), SERCA2, and SERCA3 proteins, along with a reduction in endoplasmic reticulum (ER) calcium content. Given the well-established functions of Bcl-2 family proteins and ER calcium in drug resistance, our results suggest that the down-regulation of Mcl-1 and the up-regulation of Noxa and Bim along with the decrease in ER calcium content are likely responsible for CXL017-induced resensitization of MDR cancer cells. These data also demonstrate the unique potential of CXL017 to overcome MDR in cancer treatment.

Glucocorticoid elevation of dexamethasone-induced gene 2 (Dig2/RTP801/REDD1) protein mediates autophagy in lymphocytes

Glucocorticoid hormones, including dexamethasone, induce apoptosis in lymphocytes and consequently are used clinically as chemotherapeutic agents in many hematologic malignancies. Dexamethasone also induces autophagy in lymphocytes, although the mechanism is not fully elucidated. Through gene expression analysis, we found that dexamethasone induces the expression of a gene encoding a stress response protein variously referred to as Dig2, RTP801, or REDD1. This protein is reported to inhibit mammalian target of rapamycin (mTOR) signaling. Because autophagy is one outcome of mTOR inhibition, we investigated the hypothesis that Dig2/RTP801/REDD1 elevation contributes to autophagy induction in dexamethasone-treated lymphocytes. In support of this hypothesis, RNAi-mediated suppression of Dig2/RTP801/REDD1 reduces mTOR inhibition and autophagy in glucocorticoid-treated lymphocytes. We observed similar results in Dig2/Rtp801/Redd1 knock-out murine thymocytes treated with dexamethasone. Dig2/RTP801/REDD1 knockdown also leads to increased levels of dexamethasone-induced cell death, suggesting that Dig2/RTP801/REDD1-mediated autophagy promotes cell survival. Collectively, these findings demonstrate for the first time that elevation of Dig2/RTP801/REDD1 contributes to the induction of autophagy.

The BCL-2 5' untranslated region contains an RNA G-quadruplex-forming motif that modulates protein expression

The BCL-2 gene encodes a 25 kDa membrane protein that plays critical roles in the control of apoptosis. The regulation of BCL-2 gene expression is highly complex and occurs both transcriptionally and posttranscriptionally. In particular, the 5' upstream region of BCL-2 contains a number of elements that control its expression. We have identified a highly conserved 25-nucleotide G-rich sequence (BCL2Q), with potential to fold into a RNA G-quadruplex structure, located 42 nucleotides upstream of the translation start site of human BCL-2. In this study, we used a series of biophysical experiments to show that the BCL2Q sequence folds into a stable RNA G-quadruplex in vitro, and we conducted functional luciferase reporter-based assays, in a cell-free lysate and in three types of human cell lines, to demonstrate that the BCL2Q sequence modulates protein expression in the context of the 493-nucleotide native 5' untranslated region of BCL-2.

Identification of genes putatively involved in the pathogenesis of diffuse large B-cell lymphomas by integrative genomics

Diffuse large B-cell lymphomas (DLBCL) are highly heterogeneous with regard to clinical presentation and outcome. DLBCL copy number aberrations have been identified previously, of which the deletion at 6q21-24 was significantly associated with a highly favorable clinical response to chemotherapy. In this study, we aimed to identify genes implicated in this and other genomic regions with recurrent losses and/or gains. To identify implicated genes, we superimposed array comparative genomic hybridization (aCGH) data onto a microarray expression dataset of 42 clinically well-characterized primary nodal DLBCL biopsies. We confirmed that loss of 6q21-24 is significantly associated with a highly favorable clinical response to chemotherapy. Our approach identified 316 significant genes restricted to 32 chromosomal regions, including 24 genes identified at 6q21-24. In an independent dataset, 18% of overexpressed genes in gained regions and 55% of down-regulated genes in deleted regions were validated. In summary, using integrative genomics novel onco and tumor suppressor genes were identified in DLBCL that were not recognized by expression profiling alone.

Apoptosis inhibition by Bcl-2 gives way to autophagy in glucocorticoid-treated lymphocytes

Glucocorticosteroid hormones, including prednisone and dexamethasone (Dex), have been used to treat lymphoid malignancies for many years because they readily induce apoptosis in immature lymphocytes lacking Bcl-2. However, elevated expression of the anti-apoptotic protein Bcl-2 inhibits apoptosis and contributes to glucocorticoid resistance. Using the Bcl-2-negative WEHI7.2 lymphoma line as an experimental model, we found that Dex not only induces apoptosis but also induces autophagy. The caspase inhibitor Z-VAD-fmk inhibited apoptosis but not autophagy in Dex-treated cells. Bcl-2 overexpression inhibited Dex-induced apoptosis even more potently than Z-VAD-fmk and, contrary to previous reports, Bcl-2 neither interacted with Beclin-1 nor inhibited autophagy. Rather, Bcl-2 overexpression facilitated detection of Dex-induced autophagy by both steady state methods and flux measurements, ostensibly due to apoptosis inhibition. Autophagy contributed to prolonged survival of Bcl-2-positive lymphoma cells following Dex treatment, as survival was reduced when autophagy was inhibited by 3-methyladenine. These findings emphasize the important interplay between apoptosis and autophagy and suggest a novel mechanism by which Bcl-2, which is frequently elevated in lymphoid malignancies, contributes to glucocorticoid resistance and survival of lymphoma cells.

Bcl-2 antagonist apogossypol (NSC736630) displays single-agent activity in Bcl-2-transgenic mice and has superior efficacy with less toxicity compared with gossypol (NSC19048)

Altered expression of Bcl-2 family proteins plays central roles in apoptosis dysregulation in cancer and leukemia, promoting malignant cell expansion and contributing to chemoresistance. In this study, we compared the toxicity and efficacy in mice of natural product gossypol and its semisynthetic derivative apo-gossypol, compounds that bind and inhibit antiapoptotic Bcl-2 family proteins. Daily oral dosing studies showed that mice tolerate doses of apogossypol 2- to 4-times higher than gossypol. Hepatotoxicity and gastrointestinal toxicity represented the major adverse activities of gossypol, with apogossypol far less toxic. Efficacy was tested in transgenic mice in which Bcl-2 is overexpressed in B cells, resembling low-grade follicular lymphoma in humans. In vitro, Bcl-2-expressing B cells from transgenic mice were more sensitive to cytotoxicity induced by apogossypol than gossypol, with LD50 values of 3 to 5 microM and 7.5 to 10 microM, respectively. In vivo, using the maximum tolerated dose of gossypol for sequential daily dosing, apogossypol displayed superior activity to gossypol in terms of reducing splenomegaly and reducing B-cell counts in spleens of Bcl-2-transgenic mice. Taken together, these studies indicate that apogossypol is superior to parent compound gossypol with respect to toxicology and efficacy, suggesting that further development of this compound for cancer therapy is warranted.

Gene therapy for carcinoma of the breast

In view of the limited success of available treatment modalities for breast cancer, alternative and complementary strategies need to be developed. The delineation of the molecular basis of breast cancer provides the possibility of specific intervention by gene therapy through the introduction of genetic material for therapeutic purposes. In this regard, several gene therapy approaches for carcinoma of the breast have been developed. These approaches can be divided into six broad categories: (1) mutation compensation, (2) molecular chemotherapy, (3) proapoptotic gene therapy, (4) antiangiogenic gene therapy, (5) genetic immunopotentiation, and (6) genetic modulation of resistance/sensitivity. Clinical trials for breast cancer have been initiated to evaluate safety, toxicity, and efficacy. Combined modality therapy with gene therapy and chemotherapy or radiation therapy has shown promising results. It is expected that as new therapeutic targets and approaches are identified and advances in vector design are realized, gene therapy will play an increasing role in clinical breast cancer treatment.

Critical upstream signals of cytochrome C release induced by a novel Bcl-2 inhibitor

Cytochrome c release is a central step in the apoptosis induced by many death stimuli. Bcl-2 plays a critical role in controlling this step. In this study, we investigated the upstream mechanism of cytochrome c release induced by ethyl 2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate (HA14-1), a recently discovered small molecule inhibitor of Bcl-2. HA14-1 was found to induce cytochrome c release from the mitochondria of intact cells but not from isolated mitochondria. Cytochrome c release from isolated mitochondria requires the presence of both HA14-1 and exogenous Ca(2+). This suggests that both mitochondrial and extramitochondrial signals are important. In intact cells, treatment with HA14-1 caused Ca(2+) spike, change in mitochondrial membrane potential (Delta psi(m)) transition, Bax translocation, and reactive oxygen species (ROS) generation prior to cytochrome c release. Pretreatment with either EGTA acetoxymethyl ester or vitamin E resulted in a significant decrease in cytochrome c release and cell death induced by HA14-1. Furthermore pretreatment with RU-360, an inhibitor of the mitochondrial Ca(2+) uniporter, or with EGTA acetoxymethyl ester, but not with vitamin E, prevented the HA14-1-induced Delta psi(m) transition and Bax translocation. This suggests that ROS generation is an event that occurs after the Delta psi(m) transition and Bax translocation. Together these data demonstrate that the Ca(2+) spike, mitochondrial Bcl-2 presensitization, and subsequent Delta psi(m) transition, Bax translocation, and ROS generation are important upstream signals for cytochrome c release upon HA14-1 stimulation. The involvement of endoplasmic reticulum and mitochondrial signals suggests both organelles are crucial for HA14-1-induced apoptosis.

Par-4 inducible apoptosis in prostate cancer cells

Prostate cancer is associated with the inability of prostatic epithelial cells to undergo apoptosis rather than with increased cell proliferation. Prostate apoptosis response-4 (Par-4) is a unique pro-apoptotic molecule that is capable of selectively inducing apoptosis in cancer cells when over-expressed, sensitizing the cells to diverse apoptotic stimuli and causing regression of tumors in animal models. This review discusses the salient functions of Par-4 that can be harnessed to prostate cancer therapy.

Defective Bax activation in Hodgkin B-cell lines confers resistance to staurosporine-induced apoptosis

Deregulated apoptosis represents an important hallmark of tumor cells. Here we investigated the induction of cell death signaling pathways in cell lines previously established from patients with Hodgkin's disease. Our data show that Hodgkin's disease derived B-cell lines uniformly proved resistant to staurosporine, a protein kinase C inhibitor that preferentially stimulates the mitochondrial apoptotic pathway. Contrary to control cell lines, staurosporine failed to induce cytochrome c release from mitochondria in Hodgkin derived B-cells. Correspondingly, activation of caspases was not observed in these cells. In staurosporine-treated Hodgkin cells Bax remained in its inactive state, indicating that these cell lines have a defect in this crucial step in apoptotic signaling upstream of the mitochondria. Our results suggest that the failure to activate Bax might represent a common defect of Hodgkin tumor cells of the B-cell lineage.

PK11195, a peripheral benzodiazepine receptor ligand, chemosensitizes acute myeloid leukemia cells to relevant therapeutic agents by more than one mechanism

Like Bcl-2, peripheral benzodiazepine receptors (pBzRs) reside in mitochondrial pores, are frequently over-expressed in tumor cells, and can protect cells from apoptotic cell death. We now show that the high-affinity, pBzR-specific ligand, PK11195, chemosensitizes AML cells to relevant chemotherapeutics, but is relatively non-toxic as a single agent, and does not chemosensitize normal myeloid cells. PK11195 can block p-glycoprotein efflux in AMLs, contributing to increased daunomycin toxicity in efflux-competent AMLs, but can also sensitize AMLs to cytarabine and DNR-sensitize efflux-incompetent AMLs, presumably via mitochondrial pore effects documented in other models. Therefore, PK11195 might contribute to improved clinical outcomes in AML.

Chronic hypoxia induces apoptosis in cardiac myocytes: a possible role for Bcl-2-like proteins

The effect of prolonged hypoxia as well as the molecular mechanisms on cardiac cell death is not well established. A possible role of Bcl-2 and Bax in hypoxia-induced apoptosis in different cell types has been proposed. Here we demonstrate the effect of hypoxia on the induction of apoptosis and the expression of Bcl-2-like proteins in vivo and in vitro. Hearts from rats exposed to chronic hypoxia (n = 4) showed an increased rate of apoptosis compared to normoxic hearts (n = 4). The induction of apoptosis in hypoxic hearts correlated with a significant decrease of Bcl-2 protein level, whereas Bax protein expression was increased. Exposure of isolated neonatal rat cardiac myocytes to hypoxia also resulted in a significant increase in apoptosis. However, Bcl-2 and Bax protein levels essentially remained unchanged. Our results may suggest a different molecular mechanism of hypoxia-induced apoptosis in vivo and in vitro.

Primary cutaneous B-cell lymphoma: a clinical, histological, phenotypic and genotypic study of 21 cases

The clinical, histological, phenotypic and genotypic features of 21 primary cutaneous B-cell lymphomas (CBCLs) have been investigated. The patients were 13 men and eight women aged 34-91 years (median 67) at diagnosis. Eighteen patients had localized disease, and three had multiple skin lesions at diagnosis. Twelve patients developed cutaneous or extracutaneous recurrences, and five died from malignant lymphoma 7-84 months (median 36) after diagnosis. Histological examination showed features of marginal zone/mucosa-associated lymphoid tissue (MALT)-type lymphoma in 12 cases. Three of these had transformed to diffuse large B-cell lymphoma (DLBCL) in relapse biopsies. The remaining cases were seven primary DLBCLs and two cases tentatively classified as follicle centre cell (FCC) lymphoma. The neoplastic B cells showed similar phenotypes and genotypes in most cases (CD20+, CD79+, CD5-, CD10-, cyclin D1-, bcl-2+, bcl-x-, bax-, t(14;18)-negative). p53 protein was expressed in five cases, and four harboured mis-sense or loss-of-function mutations in the p53 gene. Deletion or promoter region hypermethylation of the p16INK4a gene was detected in two patients with DLBCL. The level of retinoblastoma protein expression and the proliferative fraction were significantly higher in DLBCL (> 50%) than in MALT- or FCC-type lymphomas (< 10%). Features associated with an unfavourable prognosis were the presence of multiple skin lesions at diagnosis, transformation from MALT-type lymphoma to DLBCL, and possibly p16INK4a aberrations. It is concluded that most CBCLs are dissimilar from FCC lymphomas and seem to be more closely related to marginal zone/MALT-type lymphomas. It is also suggested that there are fundamental differences between DLBCL and other histological categories of CBCL, indicating that cutaneous DLBCL is a separate entity with an increased growth potential and genetic features similar to DLBCL originating in other anatomical sites.