An inhibitor of Bcl-2 family proteins induces regression of solid tumours

Proteins in the Bcl-2 family are central regulators of programmed cell death, and members that inhibit apoptosis, such as Bcl-X(L) and Bcl-2, are overexpressed in many cancers and contribute to tumour initiation, progression and resistance to therapy. Bcl-X(L) expression correlates with chemo-resistance of tumour cell lines, and reductions in Bcl-2 increase sensitivity to anticancer drugs and enhance in vivo survival. The development of inhibitors of these proteins as potential anti-cancer therapeutics has been previously explored, but obtaining potent small-molecule inhibitors has proved difficult owing to the necessity of targeting a protein-protein interaction. Here, using nuclear magnetic resonance (NMR)-based screening, parallel synthesis and structure-based design, we have discovered ABT-737, a small-molecule inhibitor of the anti-apoptotic proteins Bcl-2, Bcl-X(L) and Bcl-w, with an affinity two to three orders of magnitude more potent than previously reported compounds. Mechanistic studies reveal that ABT-737 does not directly initiate the apoptotic process, but enhances the effects of death signals, displaying synergistic cytotoxicity with chemotherapeutics and radiation. ABT-737 exhibits single-agent-mechanism-based killing of cells from lymphoma and small-cell lung carcinoma lines, as well as primary patient-derived cells, and in animal models, ABT-737 improves survival, causes regression of established tumours, and produces cures in a high percentage of the mice.

A novel anti-apoptosis gene, survivin, expressed in cancer and lymphoma

Inhibitors of programmed cell death (apoptosis) aberrantly prolonging cell viability may contribute to cancer by facilitating the insurgence of mutations and by promoting resistance to therapy. Despite the identification of several new apoptosis inhibitors related to bcl-2 or to the baculovirus IAP gene, it is not clear whether apoptosis inhibition plays a general role in neoplasia. Here, we describe a new human gene encoding a structurally unique IAP apoptosis inhibitor, designated survivin. Survivin contains a single baculovirus IAP repeat and lacks a carboxyl-terminal RING finger. Present during fetal development, survivin is undetectable in terminally differentiated adult tissues. However, survivin becomes prominently expressed in transformed cell lines and in all the most common human cancers of lung, colon, pancreas, prostate and breast, in vivo. Survivin is also found in approximately 50% of high-grade non-Hodgkin's lymphomas (centroblastic, immunoblastic), but not in low-grade lymphomas (lymphocytic). Recombinant expression of survivin counteracts apoptosis of B lymphocyte precursors deprived of interleukin 3 (IL-3). These findings suggest that apoptosis inhibition may be a general feature of neoplasia and identify survivin as a potential new target for apoptosis-based therapy in cancer and lymphoma.

Restoration of p53 function leads to tumour regression in vivo

Tumorigenesis is a multi-step process that requires activation of oncogenes and inactivation of tumour suppressor genes. Mouse models of human cancers have recently demonstrated that continuous expression of a dominantly acting oncogene (for example, Hras, Kras and Myc) is often required for tumour maintenance; this phenotype is referred to as oncogene addiction. This concept has received clinical validation by the development of active anticancer drugs that specifically inhibit the function of oncoproteins such as BCR-ABL, c-KIT and EGFR. Identifying additional gene mutations that are required for tumour maintenance may therefore yield clinically useful targets for new cancer therapies. Although loss of p53 function is a common feature of human cancers, it is not known whether sustained inactivation of this or other tumour suppressor pathways is required for tumour maintenance. To explore this issue, we developed a Cre-loxP-based strategy to temporally control tumour suppressor gene expression in vivo. Here we show that restoring endogenous p53 expression leads to regression of autochthonous lymphomas and sarcomas in mice without affecting normal tissues. The mechanism responsible for tumour regression is dependent on the tumour type, with the main consequence of p53 restoration being apoptosis in lymphomas and suppression of cell growth with features of cellular senescence in sarcomas. These results support efforts to treat human cancers by way of pharmacological reactivation of p53.

Primary bioassay of human tumor stem cells

A simple method has been developed to support human tumor stem cell colony growth in soft agar. The technique appears suitable for culture of a variety of neoplasms of differing histopathology. Tumor stem cell colonies arising from different types of cancer have differing growth characteristics and colony morphology. This bioassay should be suitable for clinical studies of effects of anticancer drugs or irradiation on human tumor stem cells.

Role of imaging in the staging and response assessment of lymphoma: consensus of the International Conference on Malignant Lymphomas Imaging Working Group

PURPOSE

Recent advances in imaging, use of prognostic indices, and molecular profiling techniques have the potential to improve disease characterization and outcomes in lymphoma. International trials are under way to test image-based response–adapted treatment guided by early interim positron emission tomography (PET)–computed tomography (CT). Progress in imaging is influencing trial design and affecting clinical practice. In particular, a five-point scale to grade response using PET-CT, which can be adapted to suit requirements for early- and late-response assessment with good interobserver agreement, is becoming widely used both in practice- and response-adapted trials. A workshop held at the 11th International Conference on Malignant Lymphomas (ICML) in 2011 concluded that revision to current staging and response criteria was timely.

METHODS

An imaging working group composed of representatives from major international cooperative groups was asked to review the literature, share knowledge about research in progress, and identify key areas for research pertaining to imaging and lymphoma.

RESULTS

A working paper was circulated for comment and presented at the Fourth International Workshop on PET in Lymphoma in Menton, France, and the 12th ICML in Lugano, Switzerland, to update the International Harmonisation Project guidance regarding PET. Recommendations were made to optimize the use of PET-CT in staging and response assessment of lymphoma, including qualitative and quantitative methods.

CONCLUSION

This article comprises the consensus reached to update guidance on the use of PET-CT for staging and response assessment for [18F]fluorodeoxyglucose-avid lymphomas in clinical practice and late-phase trials.

Reverse engineering of regulatory networks in human B cells

Cellular phenotypes are determined by the differential activity of networks linking coregulated genes. Available methods for the reverse engineering of such networks from genome-wide expression profiles have been successful only in the analysis of lower eukaryotes with simple genomes. Using a new method called ARACNe (algorithm for the reconstruction of accurate cellular networks), we report the reconstruction of regulatory networks from expression profiles of human B cells. The results are suggestive a hierarchical, scale-free network, where a few highly interconnected genes (hubs) account for most of the interactions. Validation of the network against available data led to the identification of MYC as a major hub, which controls a network comprising known target genes as well as new ones, which were biochemically validated. The newly identified MYC targets include some major hubs. This approach can be generally useful for the analysis of normal and pathologic networks in mammalian cells.

Oncogene-induced senescence as an initial barrier in lymphoma development

Acute induction of oncogenic Ras provokes cellular senescence involving the retinoblastoma (Rb) pathway, but the tumour suppressive potential of senescence in vivo remains elusive. Recently, Rb-mediated silencing of growth-promoting genes by heterochromatin formation associated with methylation of histone H3 lysine 9 (H3K9me) was identified as a critical feature of cellular senescence, which may depend on the histone methyltransferase Suv39h1. Here we show that Emicro-N-Ras transgenic mice harbouring targeted heterozygous lesions at the Suv39h1, or the p53 locus for comparison, succumb to invasive T-cell lymphomas that lack expression of Suv39h1 or p53, respectively. By contrast, most N-Ras-transgenic wild-type ('control') animals develop a non-lymphoid neoplasia significantly later. Proliferation of primary lymphocytes is directly stalled by a Suv39h1-dependent, H3K9me-related senescent growth arrest in response to oncogenic Ras, thereby cancelling lymphomagenesis at an initial step. Suv39h1-deficient lymphoma cells grow rapidly but, unlike p53-deficient cells, remain highly susceptible to adriamycin-induced apoptosis. In contrast, only control, but not Suv39h1-deficient or p53-deficient, lymphomas senesce after drug therapy when apoptosis is blocked. These results identify H3K9me-mediated senescence as a novel Suv39h1-dependent tumour suppressor mechanism whose inactivation permits the formation of aggressive but apoptosis-competent lymphomas in response to oncogenic Ras.

Autophagy inhibition enhances therapy-induced apoptosis in a Myc-induced model of lymphoma

Autophagy is a lysosome-dependent degradative pathway frequently activated in tumor cells treated with chemotherapy or radiation. Whether autophagy observed in treated cancer cells represents a mechanism that allows tumor cells to survive therapy or a mechanism for initiating a nonapoptotic form of programmed cell death remains controversial. To address this issue, the role of autophagy in a Myc-induced model of lymphoma generated from cells derived from p53ER(TAM)/p53ER(TAM) mice (with ER denoting estrogen receptor) was examined. Such tumors are resistant to apoptosis due to a lack of nuclear p53. Systemic administration of tamoxifen led to p53 activation and tumor regression followed by tumor recurrence. Activation of p53 was associated with the rapid appearance of apoptotic cells and the induction of autophagy in surviving cells. Inhibition of autophagy with either chloroquine or ATG5 short hairpin RNA (shRNA) enhanced the ability of either p53 activation or alkylating drug therapy to induce tumor cell death. These studies provide evidence that autophagy serves as a survival pathway in tumor cells treated with apoptosis activators and a rationale for the use of autophagy inhibitors such as chloroquine in combination with therapies designed to induce apoptosis in human cancers.

Malignant lymphoma of mucosa-associated lymphoid tissue. A distinctive type of B-cell lymphoma

As illustrated in the two cases described in this paper close morphologic and immunohistochemical similarities exist between Mediterranean lymphoma (MTL) and primary gastrointestinal lymphoma of follicle center cell (FCC) origin as it occurs in Western countries. Similarities between the two conditions include a dense noninvasive monotypic lamina propria plasma cell infiltrate, present in all cases of MTL and in some cases of Western gastrointestinal FCC lymphoma, and an invasive infiltrate of FCCs morphologically distinct from the plasma cells. A distinctive lesion produced by individual gland invasion characterizes both types of lymphoma. A clonal relationship between the lamina propria plasma cells and the invasive FCCs, long suspected but never proved in MTL, can be demonstrated in Western cases. Many of the histologic and clinical features common to these lymphomas can be explained in the context of the normal maturation sequences of gut associated lymphoid tissue. It is suggested that MTL and Western cases of primary FCC gastrointestinal lymphoma share a common histogenesis from mucosa associated lymphoid tissue.

bcl-2-immunoglobulin transgenic mice demonstrate extended B cell survival and follicular lymphoproliferation

Human follicular B cell lymphomas possess a t(14;18) interchromosomal translocation that juxtaposes the putative proto-oncogene bcl-2 with the immunoglobulin (Ig) heavy chain locus. We generated minigene constructs representing the bcl-2-Ig fusion gene found at this chromosomal breakpoint. These constructs were placed into the germ line of mice to assess the effects of the t(14;18) during development. The transgene demonstrates a lymphoid pattern of expression and uniformly results in an expanded follicular center cell population. Hyperplastic splenic follicles coalesce to form massive regions of splenic white pulp. Mice over 15 weeks of age demonstrate regional lymphadenopathy with abnormal cellular infiltrates. The expanded lymphoid compartment is composed predominantly of polyclonal B220-positive, IgM/IgD-positive B cells. Provocatively, the bcl-2-Ig transgene confers a survival advantage to a population of mature B cells assessed in vitro. bcl-2-Ig transgenic mice document a prospective role for the t(14;18) in B cell growth and the pathogenesis of follicular lymphoma.

The International Consensus Classification of Mature Lymphoid Neoplasms: a report from the Clinical Advisory Committee

Since the publication of the Revised European-American Classification of Lymphoid Neoplasms in 1994, subsequent updates of the classification of lymphoid neoplasms have been generated through iterative international efforts to achieve broad consensus among hematopathologists, geneticists, molecular scientists, and clinicians. Significant progress has recently been made in the characterization of malignancies of the immune system, with many new insights provided by genomic studies. They have led to this proposal. We have followed the same process that was successfully used for the third and fourth editions of the World Health Organization Classification of Hematologic Neoplasms. The definition, recommended studies, and criteria for the diagnosis of many entities have been extensively refined. Some categories considered provisional have now been upgraded to definite entities. Terminology for some diseases has been revised to adapt nomenclature to the current knowledge of their biology, but these modifications have been restricted to well-justified situations. Major findings from recent genomic studies have impacted the conceptual framework and diagnostic criteria for many disease entities. These changes will have an impact on optimal clinical management. The conclusions of this work are summarized in this report as the proposed International Consensus Classification of mature lymphoid, histiocytic, and dendritic cell tumors.

TET2 inactivation results in pleiotropic hematopoietic abnormalities in mouse and is a recurrent event during human lymphomagenesis

Loss-of-function mutations affecting one or both copies of the Ten-Eleven-translocation (TET)2 gene have been described in various human myeloid malignancies. We report that inactivation of Tet2 in mouse perturbs both early and late steps of hematopoiesis including myeloid and lymphoid differentiation in a cell-autonomous manner, endows the cells with competitive advantage, and eventually leads to the development of malignancies. We subsequently observed TET2 mutations in human lymphoid disorders. TET2 mutations could be detected in immature progenitors endowed with myeloid colony-forming potential. Our results show that the mutations present in lymphoid tumor cells may occur at both early and later steps of lymphoid development and indicate that impairment of TET2 function or/and expression predisposes to the development of hematological malignancies.

Report of an international workshop to standardize baseline evaluation and response criteria for primary CNS lymphoma

Standardized guidelines for the baseline evaluation and response assessment of primary CNS lymphoma (PCNSL) are critical to ensure comparability among clinical trials for newly diagnosed patients. The relative rarity of this tumor precludes rapid completion of large-scale phase III trials and, therefore, our reliance on the results of well-designed phase II trials is critical. To formulate this recommendation, an international group of experts representing hematologic oncology, medical oncology, neuro-oncology, neurology, radiation oncology, neurosurgery, and ophthalmology met to review current standards of reporting and to formulate a consensus opinion regarding minimum baseline evaluation and common standards for assessing response to therapy. The response guidelines were based on the results of neuroimaging, corticosteroid use, ophthalmologic examination, and CSF cytology. A critical issue that requires additional study is the optimal method to assess the neurocognitive impact of therapy and address the quality of life of PCNSL survivors. We hope that these guidelines will improve communication among investigators and comparability among clinical trials in a way that will allow us to develop better therapies for patients.

The natural history of initially untreated low-grade non-Hodgkin's lymphomas

To learn more about the natural history of low-grade non-Hodgkin's lymphoma, we have studied 83 patients in whom the advanced disease was initially managed without therapy. Actuarial survival was 82 per cent at 5 years and 73 per cent at 10 years. The median time until therapy was required was three years. Spontaneous regressions occurred in 19 untreated patients (23 per cent), including 30 per cent of patients with nodular, poorly differentiated lymphocytic lymphoma. Histologic transformation to an intermediate-grade or high-grade lymphoma occurred both before and after primary therapy. The actuarial risk of transformation among the initially untreated patients was similar to that in a group of patients treated at this institution immediately after diagnosis. Neither the time to histologic transformation nor the incidence of transformation was influenced by when therapy was started.

Non-Hodgkin's lymphoma in 90 homosexual men. Relation to generalized lymphadenopathy and the acquired immunodeficiency syndrome

We describe the histologic and clinical features of non-Hodgkin's lymphoma diagnosed between January 1980 and December 1983 in 90 homosexual men from San Francisco, Los Angeles, Houston, and New York. The median age was 37 years, with an age distribution identical to that for cases of AIDS reported to the Centers for Disease Control. Sixty-two per cent of the patients had high-grade (aggressive) subtypes of lymphoma, 29 per cent had subtypes of intermediate grade, and 7 per cent had low-grade subtypes. Histologic subtypes and malignant cell phenotypes were consistent with a B-cell origin. All but two men had extranodal lymphoma: central-nervous-system, bone-marrow, bowel, and mucocutaneous sites were most commonly involved. Thirty-five of 66 evaluable men (53 per cent) had complete responses to combination chemotherapy or radiotherapy or both, and thus far, 19 (54 per cent) of them have had a relapse. Mortality and morbidity were closely related to prodromal manifestations; death or illness have occurred in 19 (91 per cent) of the 21 men who presented with AIDS, in 26 (79 per cent) of the 33 who presented with generalized lymphadenopathy, and in 5 (42 per cent) of the 12 who had no prodromal manifestations. Mortality rates analyzed according to histologic grade were higher than currently reported rates in other patient populations. Kaposi's sarcoma or severe opportunistic infections characteristic of AIDS developed in 14 of 33 men (42 per cent) who presented with generalized lymphadenopathy and in 3 of 12 (33 per cent) without prodromal manifestations. We conclude that non-Hodgkin's lymphoma in members of an AIDS risk group is a serious manifestation of AIDS and the AIDS-related complex.

Lymphopenia as a prognostic factor for overall survival in advanced carcinomas, sarcomas, and lymphomas

Lymphopenia is frequent in advanced cancers and predicts the toxicity of chemotherapy. Its effect on relapse and survival is uncertain. Its prognostic value for survival was analyzed in three databases of previously reported prospective multicenter studies: (a) FEC chemotherapy in metastatic breast carcinoma; (b) CYVADIC in advanced soft tissue sarcoma (European Organization for Research and Treatment of Cancer-Soft Tissue and Bone Sarcoma Group 62791); and (c) prospective, consecutive phase III studies of aggressive diffuse large-cell non-Hodgkin's lymphomas conducted at Centre Léon Bérard between 1987 and 1993. Univariate and multivariate analyses of prognostic factors for survival were performed. The incidence of lymphopenia of <1,000/microL before treatment was constant among the series: 25%, 24%, and 27%, respectively. Lymphopenia was significantly more frequent (P < 0.05) in metastatic breast cancer patients with performance status (PS) of >1, non-Hodgkin's lymphoma patients with international prognostic index (IPI) of > 0, and advanced soft tissue sarcoma and metastatic breast cancer patients with bone metastases. Inunivariate analysis, lymphopenia of <1,000/microL significantly correlated to overall survival in patients with metastatic breast cancer (median, 10 versus 14 mo; P < 0.0001), advanced soft tissue sarcoma (median, 5 versus 10 months; P < 0.01), and non-Hodgkin lymphoma (median, 11 versus 94 months; P < 0.0001). In multivariate analysis (Cox model), lymphopenia was an independent prognostic factor for overall survival in metastatic breast cancer [RR (relative risk), 1.8; 95% CI (confidence interval), 1.3-2.4] along with liver metastases and PS; in advanced soft tissue sarcoma (RR, 1.46; 95% CI, 1.0-2.1) along with liver metastases, lung metastases, and PS; and in non-Hodgkin's lymphoma (RR, 1.48; 95% CI, 1.03-2.1) along with IPI. Our findings show that lymphopenia is an independent prognostic factor for overall and progression-free survival in several cancers.

Report of the Workshop on Nasal and Related Extranodal Angiocentric T/Natural Killer Cell Lymphomas. Definitions, differential diagnosis, and epidemiology

A workshop jointly sponsored by the University of Hong Kong and the Society for Hematopathology explored the definition, differential diagnosis, and epidemiology of angiocentric lymphomas presenting in the nose and other extranodal sites. The participants concluded that nasal T/natural killer (NK) cell lymphoma is a distinct clinicopathologic entity highly associated with Epstein-Barr virus (EBV). In situ hybridization for EBV an be very valuable in early diagnosis, especially if tissue is sparse. The cytologic spectrum is broad, ranging from small or medium-sized cells to large transformed cells. Histologic progression often occurs with time. Necrosis is nearly always present, and angioinvasion by tumor cells is seen in most cases. Nasal T/NK cell lymphoma has a characteristic immunophenotype: CD2-positive, CD56-positive, but usually negative for surface CD3. Cytoplasmic CD3 can be detected in paraffin sections. Clonal T-cell receptor gene rearrangement is not found. Tumors with an identical phenotype and genotype occur in other extranodal sites, most commonly in the skin, subcutis, and gastrointestinal tract, and should be referred to as nasal-type T/NK cell lymphomas. The differential diagnosis includes lymphomatoid granulomatosis, blastic or monomorphic NK cell lymphoma/leukemia, CD56-positive peripheral T-cell lymphoma, and enteropathy-associated T-cell lymphoma.

Tumor growth need not be driven by rare cancer stem cells

The cancer stem cell hypothesis postulates that tumor growth is driven by a rare subpopulation of tumor cells. Much of the supporting evidence for this intriguing idea is derived from xenotransplantation experiments in which human leukemia cells are grown in immunocompromised mice. We show that, when lymphomas and leukemias of mouse origin are transplanted into histocompatible mice, a very high frequency (at least 1 in 10) of the tumor cells can seed tumor growth. We suggest that the low frequency of tumor-sustaining cells observed in xenotransplantation studies may reflect the limited ability of human tumor cells to adapt to growth in a foreign (mouse) milieu.

Clinical applications of PET in oncology

Positron emission tomography (PET) provides metabolic information that has been documented to be useful in patient care. The properties of positron decay permit accurate imaging of the distribution of positron-emitting radiopharmaceuticals. The wide array of positron-emitting radiopharmaceuticals has been used to characterize multiple physiologic and pathologic states. PET is used for characterizing brain disorders such as Alzheimer disease and epilepsy and cardiac disorders such as coronary artery disease and myocardial viability. The neurologic and cardiac applications of PET are not covered in this review. The major utilization of PET clinically is in oncology and consists of imaging the distribution of fluorine 18 fluorodeoxyglucose (FDG). FDG, an analogue of glucose, accumulates in most tumors in a greater amount than it does in normal tissue. FDG PET is being used in diagnosis and follow-up of several malignancies, and the list of articles supporting its use continues to grow. In this review, the physics and instrumentation aspects of PET are described. Many of the clinical applications in oncology are mature and readily covered by third-party payers. Other applications are being used clinically but have not been as carefully evaluated in the literature, and these applications may not be covered by third-party payers. The developing applications of PET are included in this review.

Hydroxyldaunomycin (Adriamycin) combination chemotherapy in malignant lymphoma

Combination chemotherapy with CHOP (cyclophosphamide, Adriamycin, vincristine, and prednisone) and HOP (Adrimycin, vincristine, and prednisone, was used as treatment for patients with pathologically staged, advanced non-Hodgkin's lymphoma. Among 204 evaluable patients treated on CHOP there were 71% complete remissions with 92% overall responses. Among the 216 evaluable patients on HOP there were 61% complete remissions and 88% responses. Complete remission rates among patients with histiocytic lymphoma were comparable to those of patients with lymphocytic disease. Patients with nodular lymphoma had higher rates of complete remission than their counterparts with diffuse lymphoma. This was noted with both CHOP (78% vs. 67%) and HOP (67% vs. 60%) induction therapy. Rapid responses were common, as more than 14% of complete remissions and 66% of overall responses were achieved with the first course of treatment. Patients in complete remission have been maintained with either cyclophosphamide, vincristine, and prednisone (COP) or arabinosyl cytosine, vincristine, and prednisone (OAP). After 1 year, 86% of patients on COP and 80% on OAP are projected to be free of disease.

Distribution of human herpesvirus-8 latently infected cells in Kaposi's sarcoma, multicentric Castleman's disease, and primary effusion lymphoma

Human herpesvirus 8 (HHV-8, also called KSHV) is linked to the etiopathogenesis of Kaposi's sarcoma (KS), multicentric Castleman's disease (MCD), and primary effusion lymphoma (PEL). The universal presence of HHV-8 in early KS has not yet been shown. We used a mAb (LN53) against latent nuclear antigen-1 (LNA-1) of HHV-8 encoded by ORF73 to study the distribution of the cell types latently infected by HHV-8 in patch, plaque, and nodular KS, MCD, and PEL. In early KS, HHV-8 is present in <10% of cells forming the walls of ectatic vessels. In nodular KS, HHV-8 is present in cells surrounding slit-like vessels and in >90% of spindle cells, but not in normal vascular endothelium. In addition, HHV-8 colocalizes with vascular endothelial growth factor receptor-3 (VEGFR-3), a marker of lymphatic and precursor endothelium. In early KS lesions, VEGFR-3 is more extensively expressed than LNA-1, indicating that HHV-8 is not inducing the proliferation of VEGFR-3-positive endothelium directly. In MCD, HHV-8 is present in mantle zone large immunoblastic B cells. No staining for LNA-1 is seen in samples from multiple myeloma, prostate cancer, and angiosarcoma, supporting the absence of any etiological link between these diseases and HHV-8.

Tumor suppressor HIC1 directly regulates SIRT1 to modulate p53-dependent DNA-damage responses

Hypermethylated in cancer 1 (HIC1) is an epigenetically regulated transcriptional repressor that functionally cooperates with p53 to suppress age-dependent development of cancer in mice. Here we show that the mechanism by which the loss of HIC1 function promotes tumorigenesis is via activating the stress-controlling protein SIRT1 and thereby attenuating p53 function. HIC1 forms a transcriptional repression complex with SIRT1 deacetylase, and this complex directly binds the SIRT1 promoter and represses its transcription. Inactivation of HIC1 results in upregulated SIRT1 expression in normal or cancer cells; this deacetylates and inactivates p53, allowing cells to bypass apoptosis and survive DNA damage. Inhibition of SIRT1 function in cells without HIC1 abolishes the resistance to apoptosis. Since aging increases promoter hypermethylation and epigenetic silencing of HIC1, we speculate that the resultant upregulation of SIRT1 may be a double-edged sword that both promotes survival of aging cells and increases cancer risk in mammals.

Lymphomas and high-grade astrocytomas: comparison of water diffusibility and histologic characteristics

PURPOSE

To determine if water diffusivity within lymphomas and high-grade astrocytomas correlates with cellularity.

MATERIALS AND METHODS

Echo-planar diffusion-weighted magnetic resonance (MR) images obtained in 11 patients with brain lymphomas (19 lesions) and in 17 patients with astrocytomas (19 lesions) were retrospectively reviewed. Regions of interest were drawn on apparent diffusion coefficient (ADC) maps in enhancing tumor. ADC values were normalized by dividing ADC values of tumors by those of normal-appearing regions and expressing the quotient as a ratio. Histologic samples from 11 patients with astrocytomas (11 lesions) and seven patients with lymphoma (seven lesions) were reviewed. Cellularity was measured by calculating the percentage of nuclear area and the percentage of cytoplasmic area and expressing the results as the nuclear-to-cytoplasmic (N/C) ratio. The ADC and N/C ratios of both tumor types were compared by using a two-tailed t test.

RESULTS

Mean ADC ratio of lymphomas was 1.15 (SD, 0.33; standard error of the mean [SEM], 0.10), and that of high-grade astrocytomas was 1.68 (SD, 0.48; SEM, 0.11) (P <.01). Mean N/C ratio of lymphoma was 1.45 (SD, 0.94; SEM, 0.36), and that of high-grade astrocytomas was 0.24 (SD, 0.18; SEM, 0.05) (P <.01).

CONCLUSION

Measurements of water diffusivity and cellularity suggest that higher cellularity contributes to more restricted diffusion.