Age-related chemosensitivity of stem cells from human malignant brain tumours

The peritumoral edema index and related mechanisms influence the prognosis of GBM patients

Background

Peritumoral brain edema (PTBE) represents a characteristic phenotype of intracranial gliomas. However, there is a lack of consensus regarding the prognosis and mechanism of PTBE. In this study, clinical imaging data, along with publicly available imaging data, were utilized to assess the prognosis of PTBE in glioblastoma (GBM) patients, and the associated mechanisms were preliminarily analyzed.

Methods

We investigated relevant imaging features, including edema, in GBM patients using ITK-SNAP imaging segmentation software. Risk factors affecting progression-free survival (PFS) and overall survival (OS) were assessed using a Cox proportional hazard regression model. In addition, the impact of PTBE on PFS and OS was analyzed in clinical GBM patients using the Kaplan-Meier survival analysis method, and the results further validated by combining data from The Cancer Imaging Archive (TCIA) and The Cancer Genome Atlas (TCGA). Finally, functional enrichment analysis based on TCIA and TCGA datasets identified several pathways potentially involved in the mechanism of edema formation.

Results

This study included a total of 32 clinical GBM patients and 132 GBM patients from public databases. Univariate and multivariate analyses indicated that age and edema index (EI) are independent risk factors for PFS, but not for OS. Kaplan-Meier curves revealed consistent survival analysis results between IE groups among both clinical patients and TCIA and TCGA patients, suggesting a significant effect of PTBE on PFS but not on OS. Furthermore, functional enrichment analysis predicted the involvement of several pathways related mainly to cellular bioenergetics and vasculogenic processes in the mechanism of PTBE formation. While these novel results warrant confirmation in a larger patient cohort, they support good prognostic value for PTBE assessment in GBM.

Conclusions

Our results indicate that a low EI positively impacts disease control in GBM patients, but this does not entirely translate into an improvement in OS. Multiple genes, signaling pathways, and biological processes may contribute to the formation of peritumoral edema in GBM through cytotoxic and vascular mechanisms.

Role of glioblastoma stem cells in cancer therapeutic resistance: a perspective on antineoplastic agents from natural sources and chemical derivatives

Glioblastoma (GBM) is the highest-grade form of glioma, as well as one of the most aggressive types of cancer, exhibiting rapid cellular growth and highly invasive behavior. Despite significant advances in diagnosis and therapy in recent decades, the outcomes for high-grade gliomas (WHO grades III-IV) remain unfavorable, with a median overall survival time of 15–18 months. The concept of cancer stem cells (CSCs) has emerged and provided new insight into GBM resistance and management. CSCs can self-renew and initiate tumor growth and are also responsible for tumor cell heterogeneity and the induction of systemic immunosuppression. The idea that GBM resistance could be dependent on innate differences in the sensitivity of clonogenic glial stem cells (GSCs) to chemotherapeutic drugs/radiation prompted the scientific community to rethink the understanding of GBM growth and therapies directed at eliminating these cells or modulating their stemness. This review aims to describe major intrinsic and extrinsic mechanisms that mediate chemoradioresistant GSCs and therapies based on antineoplastic agents from natural sources, derivatives, and synthetics used alone or in synergistic combination with conventional treatment. We will also address ongoing clinical trials focused on these promising targets. Although the development of effective therapy for GBM remains a major challenge in molecular oncology, GSC knowledge can offer new directions for a promising future.

Treatment of Glioblastoma Multiforme in Elderly Patients. Clinico-therapeutic Remarks in 22 Patients Older than 80 Years

We report our remarks on 22 patients, 80 years of age and older, who were treated for glioblastoma multiforme. The 16 patients who underwent a multimodality treatment (surgery + radiotherapy + chemotherapy) had an average survival of 16.7 months versus the 5.8 months of the 8 patients treated with biopsy followed by radiotherapy and/or chemotherapy (log-rank test, P <0.001). Moreover, we point out the importance of MGMT hypermethylation as a significant prognostic factor: the 9 patients with nonmethylated MGMT had a mean survival of 7.7 months vs 17.9 months of the 13 patients with the MGMT promoter methylated (log-rank test, P = 0.0006). Several studies have pointed out age as an important negative factor for the outcome of elderly patients affected by glioblastoma multiforme. Elderly patients with a diagnosis of glioblastoma multiforme are thus generally excluded from clinical trials of treatment for the neoplasm, because it is a common opinion that the prognosis for such patients is particularly poor. On the contrary, according to our clinical and surgical experience, we firmly believe that patients older than 80 years with a histologically proven diagnosis of glioblastoma multiforme and in good health conditions (Karnofsky performance status >60) should be treated in the same way as younger patients.

Glioblastoma in Elderly Patients: Current Management and Future Perspectives

The incidence of glioblastoma (GBM) in the elderly population is slowly increasing in Western countries. Current management includes surgery, radiation therapy (RT) and chemotherapy; however, survival is significantly worse than that observed in younger patients and the optimal treatment in terms of efficacy and safety remains a matter of debate. Surgical resection is often employed as initial treatment for elderly patients with GBM, although the survival benefit is modest. Better survival has been reported in elderly patients treated with RT compared with those receiving supportive care alone, with similar survival outcome for patients undergoing standard RT (60 Gy over 6 weeks) and hypofractionated RT (25⁻40 Gy in 5⁻15 daily fractions). Temozolomide, an alkylating agent, may represent an effective and safe therapy in patients with promoter methylation of O⁶-methylguanine-DNA-methyltransferase (MGMT) gene which is predictor of responsiveness to alkylating agents. An abbreviated course of RT, 40 Gy in 15 daily fractions in combination with adjuvant and concomitant temozolomide has emerged as an effective treatment for patients aged 65 years old or over with GBM. Results of the National Cancer Institute of Canada Clinical Trials Group (NCIC CTG CE6) and European Organization for Research and Treatment of Cancer (EORTC 26062/22061) randomized study of short-course RT with or without concurrent and adjuvant temozolomide have demonstrated a significant improvement in progression-free survival and overall survival for patients receiving RT and temozolomide over RT alone, without impairing either quality of life or functional status. Although combined chemoradiation has become the recommended treatment in fit elderly patients with GBM, several questions remain unanswered, including the survival impact of chemoradiation in patients with impaired neurological status, advanced age (>75⁻80 years old), or for those with severe comorbidities. In addition, the efficacy and safety of alternative therapeutic approaches according to the methylation status of the O⁶-methylguanine-DNA methyl-transferase (MGMT) gene promoter need to be explored in future trials.

Cell Cycle Dynamics in Glioma Cancer Stem Cells

Cancer stem cells, sometimes referred to as tumor initiating cells, play pivotal roles in tumor initiation, progression, metastasis, resistance to therapy, and relapse. Understanding how these populations of cells expand in response to a host of conditions is critical in determining effective cancer therapeutics. A defining feature of cancer stem cells is the ability to switch between modes of quiescence and symmetric/asymmetric division to protect and conserve the population, this feature is traditionally reserved for normal adult stem cell populations. Understanding how the core cell cycle machinery responds to external cues to drive symmetric/asymmetric division vs. quiescence will reveal fundamental information about how cancer stem cell populations survive and expand. This chapter will describe methods to study the cell cycle dynamics in brain cancer stem cell populations and how they compare to the other populations in a tumor.

The Impact of the Tumor Microenvironment on the Properties of Glioma Stem-Like Cells

Glioblastoma is the most common and highly malignant primary brain tumor, and patients affected with this disease exhibit a uniformly dismal prognosis. Glioma stem-like cells (GSCs) are a subset of cells within the bulk tumor that possess self-renewal and multi-lineage differentiation properties similar to somatic stem cells. These cells also are at the apex of the cellular hierarchy and cause tumor initiation and expansion after chemo-radiation. These traits make them an attractive target for therapeutic development. Because GSCs are dependent on the brain microenvironment for their growth, and because non-tumorigenic cell types in the microenvironment can influence GSC phenotypes and treatment response, a better understanding of these cell types is needed. In this review, we provide a focused overview of the contributions from the microenvironment to GSC homing, maintenance, phenotypic plasticity, and tumor initiation. The interaction of GSCs with the vascular compartment, mesenchymal stem cells, immune system, and normal brain cell types are discussed. Studies that provide mechanistic insight into each of these GSC–microenvironment interactions are warranted in the future.

Choosing Wisely: a neurosurgical perspective on neuroimaging for headaches

Multiple national initiatives seek to curb spending to address increasing healthcare costs in the United States. The Choosing Wisely initiative is a popular initiative that focuses on reducing healthcare spending by setting guidelines to limit tests and procedures requested by patients and ordered by physicians. To reduce spending on neuroimaging, the Choosing Wisely initiative and other organizations have offered guidelines to limit neuroimaging for headaches. Although the intentions are laudable, these guidelines are inconsistent with the neurosurgeon's experience with patients with brain tumor. If adopted by governing or funding organizations, these guidelines threaten to negatively affect the care and outcomes of patients with brain tumors, who frequently present with minimal symptoms or isolated headaches syndromes. As physicians grapple with the difficult conflict between evidence-based cost-cutting guidelines and individualized patient-tailored medicine, they must carefully balance the costs and benefits of discretionary services such as neuroimaging for headaches. By participating in the development of validated clinical decision rules on neuroimaging for headaches, neurosurgeons can advocate for their patients and improve their patients' outcomes.

Radiation therapy for older adults with glioblastoma: radical treatment, palliative treatment, or no treatment at all?

The incidence of glioblastoma in older adults has increased over the last few decades. Current treatment includes surgery, radiotherapy, and chemotherapy, but optimal disease management remains a matter of debate. Both standard (60 Gy in 30 daily fractions) and hypofractionated radiotherapy (30-40 Gy in 10-15 daily fractions) have been employed with a similar survival benefit. Recent randomized studies indicate that chemotherapy with the alkylating agent temozolomide is a safe and effective therapeutic option for patients aged 60 years or older with newly diagnosed glioblastoma, suggesting that it should be a sufficient treatment for patients presenting with a methylated O6-methylguanine-DNA methyltransferase (MGMT) promoter gene. The addition of concomitant temozolomide chemotherapy, adjuvant temozolomide chemotherapy, or both to postoperative radiotherapy, which is the standard treatment for adults with glioblastoma, has been associated with a survival benefit for older patients with a good performance status; however, aggressive treatment in this population may be associated with a high risk of neurological toxicity and deterioration of quality of life. Survival stratification according to age, MGMT promoter methylation status, and neurological status may be useful for clinical decision making and designing randomized trials for adequately evaluating the optimal combination of radiotherapy and chemotherapy for older patients with glioblastoma.

Recommendations for the management of malignant gliomas in the elderly

According to epidemiological estimations, the elderly are going to constitute an increasing proportion of patients with gliomas in the near future. Predominantly glioblastoma histology with invariably fatal outcome, disabling comorbidities and presumed low tolerability of radiochemotherapeutic treatments are the main reasons why elderly patients have been under-represented in the majority of neuro-oncological clinical trials conducted so far. Some small retrospective studies have reported that patients with good performance status receiving surgery plus radiotherapy, and sometimes chemotherapy, may achieve a survival comparable with that of younger patients, however, in the absence of randomized studies, the balance of benefits and adverse effects of aggressive treatments remains controversial. Multidisciplinary evaluation of prognostic factors, such as performance status, cognitive functions, tumor operability and burden of comorbidities, appears to be mandatory in order to choose which patients must not be deprived of an integrated treatment with surgery, full-dose radiotherapy and chemotherapy, and which patients may reasonably be given a shorter radiotherapy plan, or even no treatment at all due to the rapidly fatal course of their disease. Peculiar features of malignant gliomas in the elderly and some practical recommendations of management will be presented and discussed in this review.

Response of primary glioblastoma cells to therapy is patient specific and independent of cancer stem cell phenotype

BACKGROUND

Glioblastoma multiforme (GBM) contains a population of cells that exhibit stem cell phenotypes. These cancer stem cells (CSCs) may be a source of therapeutic resistance, although support for this important concept is limited.

METHODS

We determined whether early-passage GBM CSCs respond differently than patient-matched, genotypically similar non-CSCs to clinically relevant single or serial doses of temozolomide (TMZ), radiation therapy (XRT), or alternating TMZ treatment and XRT, which is the standard of care for GBM patients.

RESULTS

Despite the phenotypic differences, including the presence of stem cell markers and formation of intracranial tumors, the CSCs and matched non-CSCs were equally resistant to TMZ in a majority of patients, using 2 independent assays. TMZ response was consistent with methylated O(6)-DNA methylguanine-methyltransferase (MGMT) and MGMT protein levels in both culture types. In contrast, CSCs were unexpectedly more responsive to XRT compared with matched non-CSCs from 2 patients despite having relatively equal resistance to TMZ. However, for the majority of culture pairs from individual patients, responses in CSCs were indistinguishable from non-CSC cultures.

CONCLUSIONS

In our patient-matched primary cultures, response to TMZ was tightly linked to the individual tumor's MGMT status and independent of their phenotypic differences. TMZ and XRT together revealed no additive benefit compared with monotherapy for either culture type, in contrast to the notion that the CSC population is more resistant to XRT. If the tumor cell response in vitro mirrors therapeutic response in larger patient cohorts, these rapid assays in primary cultures could allow -empirical selection of efficacious therapeutic agents on a patient-specific basis.

Whole brain radiation-induced cognitive impairment: pathophysiological mechanisms and therapeutic targets

Radiation therapy, the most commonly used for the treatment of brain tumors, has been shown to be of major significance in tu-mor control and survival rate of brain tumor patients. About 200,000 patients with brain tumor are treated with either partial large field or whole brain radiation every year in the United States. The use of radiation therapy for treatment of brain tumors, however, may lead to devastating functional deficits in brain several months to years after treatment. In particular, whole brain radiation therapy results in a significant reduction in learning and memory in brain tumor patients as long-term consequences of treatment. Although a number of in vitro and in vivo studies have demonstrated the pathogenesis of radiation-mediated brain injury, the cel-lular and molecular mechanisms by which radiation induces damage to normal tissue in brain remain largely unknown. Therefore, this review focuses on the pathophysiological mechanisms of whole brain radiation-induced cognitive impairment and the iden-tification of novel therapeutic targets. Specifically, we review the current knowledge about the effects of whole brain radiation on pro-oxidative and pro-inflammatory pathways, matrix metalloproteinases (MMPs)/tissue inhibitors of metalloproteinases (TIMPs) system and extracellular matrix (ECM), and physiological angiogenesis in brain. These studies may provide a foundation for defin-ing a new cellular and molecular basis related to the etiology of cognitive impairment that occurs among patients in response to whole brain radiation therapy. It may also lead to new opportunities for therapeutic interventions for brain tumor patients who are undergoing whole brain radiation therapy.

Presentation, management, and outcome of newly diagnosed glioblastoma in elderly patients

Object

Optimum management for elderly patients with newly diagnosed glioblastoma (GBM) in the temozolomide (TMZ) era is not well defined. The object of this study was to clarify outcomes in this population.

Methods

The authors retrospectively reviewed 105 consecutive cases involving elderly patients (age ≥ 65 years) with newly diagnosed GBM who were treated at the Mayo Clinic between 2003 and 2008.

Results

The patients' median age was 74 years (range 66–87 years), and the median Karnofsky Performance Status (KPS) score was 80 (range 40–90). Half of the patients underwent biopsy and half underwent resection. Patients with deep-seated lesions (19 patients [18%]) or multifocal lesions (34 patients [32%]) were more likely to have biopsy than resection (p = 0.0001 and 0.0009, respectively). New persistent neurological deficits developed in 7 patients (6.7%). Postoperative hemorrhage occurred in 6 patients (5.7%), all of whom underwent biopsy. Complete follow-up data regarding adjuvant treatment was available in 84 patients. Forty-one (49%) were treated with chemotherapy (mostly TMZ) and radiation therapy (RT), and 23 (27%) with RT alone. Nineteen (23%) received only palliative care after surgery (more common with biopsy, p = 0.03). Chemotherapy complications occurred in 28.6% (Grade 3 or 4 hematological complications in 11.9%). The median values for progression-free survival (PFS) and overall survival (OS) were 3.5 and 5.5 months. In a multivariate analysis, younger age (p = 0.03, risk ratio [RR] 0.34, 95% CI 0.13–0.89), single lesion (p = 0.02, RR 0.51, 95% CI 0.30–0.89), resection (p = 0.04, RR 0.54, 95% CI 0.31–0.94), and adjuvant treatment (p = 0.0001, RR 0.24, 95% CI 0.11–0.49) were associated with better OS. Only adjuvant treatment was significantly associated with prolonged PFS (p = 0.0007, RR 0.27, 95% CI 0.13–0.57). With combined therapy with resection, RT, and chemotherapy, the median PFS and OS were 8 and 12.5 months, respectively.

Conclusions

The prognosis for GBM worsens with increasing age in elderly patients. With important risks, resection and adjuvant treatment are associated with prolonged survival. Although selection bias cannot be excluded in this retrospective study, advanced age alone should not necessarily preclude optimal resection followed by adjuvant radiochemotherapy.

Increased age of transformed mouse neural progenitor/stem cells recapitulates age-dependent clinical features of human glioma malignancy

Increasing age is the most robust predictor of greater malignancy and treatment resistance in human gliomas. However, the adverse association of clinical course with aging is rarely considered in animal glioma models, impeding delineation of the relative importance of organismal versus progenitor cell aging in the genesis of glioma malignancy. To address this limitation, we implanted transformed neural stem/progenitor cells (NSPCs), the presumed cells of glioma origin, from 3- and 18-month-old mice into 3- and 20-month host animals. Transplantation with progenitors from older animals resulted in significantly shorter (P ≤ 0.0001) median survival in both 3-month (37.5 vs. 83 days) and 20-month (38 vs. 67 days) hosts, indicating that age-dependent changes intrinsic to NSPCs rather than host animal age accounted for greater malignancy. Subsequent analyses revealed that increased invasiveness, genomic instability, resistance to therapeutic agents, and tolerance to hypoxic stress accompanied aging in transformed NSPCs. Greater tolerance to hypoxia in older progenitor cells, as evidenced by elevated HIF-1 promoter reporter activity and hypoxia response gene (HRG) expression, mirrors the upregulation of HRGs in cohorts of older vs. younger glioma patients revealed by analysis of gene expression databases, suggesting that differential response to hypoxic stress may underlie age-dependent differences in invasion, genomic instability, and treatment resistance. Our study provides strong evidence that progenitor cell aging is responsible for promoting the hallmarks of age-dependent glioma malignancy and that consideration of progenitor aging will facilitate development of physiologically and clinically relevant animal models of human gliomas.

Hypofractionated Radiotherapy and Stereotactic Boost with Concurrent and Adjuvant Temozolamide for Glioblastoma in Good Performance Status Elderly Patients - Early Results of a Phase II Trial

Glioblastoma Multiforme (GBM) is an aggressive primary brain neoplasm with dismal prognosis. Based on successful phase III trials, 60 Gy involved-field radiotherapy in 30 fractions over 6 weeks [Standard radiation therapy (RT)] with concurrent and adjuvant temozolomide is currently the standard of care. In this disease, age and Karnofsky Performance Status (KPS) are the most important prognostic factors. For elderly patients, clinical trials comparing standard RT with radiotherapy abbreviated to 40 Gy in 15 fractions over 3 weeks demonstrated similar outcomes, indicating shortened radiotherapy may be an appropriate option for elderly patients. However, these trials did not include temozolomide chemotherapy, and included patients with poor KPS, possibly obscuring benefits of more aggressive treatment for some elderly patients. We conducted a prospective Phase II trial to examine the efficacy of a hypofractionated radiation course followed by a stereotactic boost with concurrent and adjuvant temozolomide chemotherapy in elderly patients with good performance status. In this study, patients 65 years and older with a KPS > 70 and histologically confirmed GBM received 40 Gy in 15 fractions with 3D conformal technique followed by a 1–3 fraction stereotactic boost to the enhancing tumor. All patients also received concurrent and adjuvant temozolomide. Patients were evaluated 1 month post-treatment and every 2 months thereafter. Between 2007 and 2010, 20 patients (9 males and 11 females) were enrolled in this study. The median age was 75.4 years (range 65–87 years). At a median follow-up of 11 months (range 7–32 months), 12 patients progressed and 5 are alive. The median progression free survival was 11 months and the median overall survival was 13 months. There was no additional toxicity. These results indicate that elderly patients with good KPS can achieve outcomes comparable to the current standard of care using an abbreviated radiotherapy course, radiosurgery boost, and temozolomide.

Resistance of glioblastoma-initiating cells to radiation mediated by the tumor microenvironment can be abolished by inhibiting transforming growth factor-β

The poor prognosis of glioblastoma (GBM) routinely treated with ionizing radiation (IR) has been attributed to the relative radioresistance of glioma-initiating cells (GIC). Other studies indicate that although GIC are sensitive, the response is mediated by undefined factors in the microenvironment. GBM produce abundant transforming growth factor-β (TGF-β), a pleotropic cytokine that promotes effective DNA damage response. Consistent with this, radiation sensitivity, as measured by clonogenic assay of cultured murine (GL261) and human (U251, U87MG) glioma cell lines, increased by approximately 25% when treated with LY364947, a small-molecule inhibitor of TGF-β type I receptor kinase, before irradiation. Mice bearing GL261 flank tumors treated with 1D11, a pan-isoform TGF-β neutralizing antibody, exhibited significantly increased tumor growth delay following IR. GL261 neurosphere cultures were used to evaluate GIC. LY364947 had no effect on the primary or secondary neurosphere-forming capacity. IR decreased primary neurosphere formation by 28%, but did not reduce secondary neurosphere formation. In contrast, LY364947 treatment before IR decreased primary neurosphere formation by 75% and secondary neurosphere formation by 68%. Notably, GL261 neurospheres produced 3.7-fold more TGF-β per cell compared with conventional culture, suggesting that TGF-β production by GIC promotes effective DNA damage response and self-renewal, which creates microenvironment-mediated resistance. Consistent with this, LY364947 treatment in irradiated GL261 neurosphere-derived cells decreased DNA damage responses, H2AX and p53 phosphorylation, and induction of self-renewal signals, Notch1 and CXCR4. These data motivate the use of TGF-β inhibitors with radiation to improve therapeutic response in patients with GBM.

Increased re-entry into cell cycle mitigates age-related neurogenic decline in the murine subventricular zone

Although new neurons are produced in the subventricular zone (SVZ) of the adult mammalian brain, fewer functional neurons are produced with increasing age. The age-related decline in neurogenesis has been attributed to a decreased pool of neural progenitor cells (NPCs), an increased rate of cell death, and an inability to undergo neuronal differentiation and develop functional synapses. The time between mitotic events has also been hypothesized to increase with age, but this has not been directly investigated. Studying primary-cultured NPCs from the young adult and aged mouse forebrain, we observe that fewer aged cells are dividing at a given time; however, the mitotic cells in aged cultures divide more frequently than mitotic cells in young cultures during a 48-hour period of live-cell time-lapse imaging. Double-thymidine-analog labeling also demonstrates that fewer aged cells are dividing at a given time, but those that do divide are significantly more likely to re-enter the cell cycle within a day, both in vitro and in vivo. Meanwhile, we observed that cellular survival is impaired in aged cultures. Using our live-cell imaging data, we developed a mathematical model describing cell cycle kinetics to predict the growth curves of cells over time in vitro and the labeling index over time in vivo. Together, these data surprisingly suggest that progenitor cells remaining in the aged SVZ are highly proliferative.

Aging attenuates radiation-induced expression of pro-inflammatory mediators in rat brain

The present study was designed to examine the effect of aging on radiation-induced expression of pro-inflammatory mediators in rat brain. Male F344xBN rats (4, 16, and 24 months of age) received either whole brain irradiation with a single dose of 10Gy gamma-rays or sham-irradiation, and were maintained for 4, 8, and 24h post-irradiation. The mRNA expression levels of various pro-inflammatory mediators such as cytokines, adhesion molecules, chemokine, and matrix metalloproteinase were analyzed by quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR). The acute inflammatory responses to irradiation, including overexpression of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), interleukin-6 (IL-6), intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), E-selectin, monocyte chemoattractant protein-1 (MCP-1), and matrix metalloproteinase-9 (MMP-9) were markedly attenuated in the hippocampus of middle-aged and old rats compared with young groups. Specifically, a significant age-dependent decrease in TNF-alpha expression was detected 8 and 24h after irradiation and a similar age-related attenuation was observed in IL-1beta, ICAM-1, and VCAM-1 expression 4 and 8h post-irradiation. MCP-1 expression was reduced 4h post-irradiation and MMP-9 expression at 8h post-irradiation. These results provide evidence for the first time that radiation-induced pro-inflammatory responses in the brain are suppressed in aged animals.

Primary brain tumors, neural stem cell, and brain tumor cancer cells: where is the link?

The discovery of brain tumor-derived cells (BTSC) with the properties of stem cells has led to the formulation of the hypothesis that neural stem cells could be the cell of origin of primary brain tumors (PBT). In this review we present the most common molecular changes in PBT, define the criteria of identification of BTSC and discuss the similarities between the characteristics of these cells and those of the endogenous population of neural stem cells (NPCs) residing in germinal areas of the adult brain. Finally, we propose possible mechanisms of cancer initiation and progression and suggest a model of tumor initiation that includes intrinsic changes of resident NSC and potential changes in the microenvironment defining the niche where the NSC reside.

DNA repair and resistance of gliomas to chemotherapy and radiotherapy

The importance of DNA repair as a resistance mechanism in gliomas, the most aggressive form of brain tumor, is a clinically relevant topic. Recent studies show that not all cells are equally malignant in gliomas. Certain subpopulations are particularly prone to drive tumor progression and resist chemo- and radiotherapy. Those cells have been variably named cancer stem cells or cancer-initiating cells or tumor-propagating cells, owing to their possible (but still uncertain) origin from normal stem cells. Although DNA repair reduces the efficacy of chemotherapeutics and ionizing radiation toward bulk gliomas, its contribution to resistance of the rare glioma stem cell subpopulations is less clear. Mechanisms other than DNA repair (in particular low proliferation and activation of the DNA damage checkpoint response) are likely main players of resistance in glioma stem cells and their targeting might yield significant therapeutic gains.

A syngeneic glioma model to assess the impact of neural progenitor target cell age on tumor malignancy

Human glioma incidence, malignancy, and treatment resistance are directly proportional to patient age. Cell intrinsic factors are reported to contribute to human age-dependent glioma malignancy, but suitable animal models to examine the role of aging are lacking. Here, we developed an orthotopic syngeneic glioma model to test the hypothesis that the age of neural progenitor cells (NPCs), presumed cells of glioma origin, influences glioma malignancy. Gliomas generated from transformed donor 3-, 12-, and 18-month-old NPCs in same-aged adult hosts formed highly invasive glial tumors that phenocopied the human disease. Survival analysis indicated increased malignancy of gliomas generated from older 12- and 18-month-old transformed NPCs compared with their 3-month counterparts (median survival of 38.5 and 42.5 vs. 77 days, respectively). This study showed for the first time that age of target cells at the time of transformation can affect malignancy and demonstrated the feasibility of a syngeneic model using transformed NPCs for future examination of the relative impacts of age-related cell intrinsic and cell-extrinsic factors in glioma malignancy.

Identification of A2B5+CD133- tumor-initiating cells in adult human gliomas

OBJECTIVE

Several studies have shown that human gliomas contain a small population of cells with stem cell-like features. It has been proposed that these "cancer stem cells" may be uniquely responsible for glioma formation and recurrence. However, human gliomas also contain an abundance of cells that closely resemble more differentiated glial progenitors. Animal model studies have shown that these cells also possess the capacity to form malignant gliomas.

METHODS

To investigate the contributions of stem-like and progenitor-like cells in human gliomas, we used flow cytometry to characterize the expression of a cancer stem cell marker (CD133) and a glial progenitor marker (A2B5) in 25 tumors. We found that human gliomas consistently express A2B5 in a large percentage of cells (61.7 +/- 3.8%, standard error of the mean). In contrast, CD133 expression was less abundant and less consistent (14.8 +/- 3.6%, standard error of the mean), with several glioblastomas containing very few or no detectable CD133+ cells. When present, the CD133+ population was almost entirely contained within the A2B5+ population. Thus, most gliomas could be divided into three distinct populations on the basis of these markers (A2B5+CD133+, A2B5+CD133-, and A2B5-CD133-). To test the tumorigenic potential of these populations, we separated cells from six tumors by fluorescence-activated cell sorting and reinjected them into nude rats.

RESULTS

We found that the capacity for these different populations to form tumors varied depending on the human tumor specimen from which they were isolated. Of the six human gliomas tested, four contained A2B5+/CD133- cells that formed tumors when transplanted into nude rats, three contained A2B5+/CD133+ cells that formed tumors, and only one glioma contained A2B5-/CD133- cells with the capacity to form tumors.

CONCLUSION

Together, these results demonstrate that human gliomas contain multiple populations of cells with the capacity to form tumors and specifically identify a population of tumorigenic A2B5+ cells that are phenotypically distinct from CD133+ cells.

Collagen gel matrix assay as an in vitro chemosensitivity test for malignant astrocytic tumors

BACKGROUND

The efficacy of individual chemotherapy based on chemosensitivity has scarcely been studied.

METHODS

We examined the chemosensitivites for four anticancer agents - 1-(4-amino-2-methyl-5-pyrimidinyl) methyl-3 (2-chloroethyl)-3-nitrosourea hydrochloride (ACNU), carboplatin, cisplatin, and etoposide - of 43 malignant astrocytic tumors (21 anaplastic astrocytomas and 22 glioblastomas) by using a collagen gel matrix assay, and we also determined the survival periods of the tumor-bearing patients. The chemosensitivity was evaluated in terms of the growth inhibition rate, using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) method.

RESULTS

For the anaplastic astrocytomas, the mean growth inhibitory rate was 33.2% with cisplatin, 37.2% with carboplatin, 28.0% with ACNU, and 24.8% with etoposide. For the glioblastomas, these rates were 36.9%, 42.3%, 23.2%, and 34.8%, respectively. The median overall and progression-free survivals of anaplastic astrocytoma-bearing patients who had undergone chemotherapy with two anticancer drugs, both of which showed significant anticancer activity (growth inhibitory rate >30%) were significantly longer than those of the patients who had been treated with two drugs, one or both of which did not show significant anticancer activity. On the other hand, there was no significant difference in the overall or the progression-free survivals in the two corresponding groups of glioblastoma-bearing patients.

CONCLUSION

The collagen gel matrix assay is clinically useful to determine in vitro chemosensitivity that reflects in vivo chemosensitivity. Individual chemotherapy for malignant astrocytic tumors, based on chemosensitivity data, could contribute to longer survival, particularly in anaplastic astrocytoma-bearing patients.

Age and bromodeoxyuridine labelling index as prognostic factors in high-grade gliomas treated with surgery and radiotherapy

AIMS

To determine the prognostic value of proliferative potential and DNA ploidy in 72 brain tumours (36 grade III and 36 grade IV astrocytomas) using bromodeoxyuridine (BrdUrd) incorporation and flow cytometry.

MATERIAL AND METHODS

All 72 patients underwent excision, mostly incomplete of the tumour. After surgery, eight patients received conventionally fractionated radiotherapy, 11 patients received accelerated radiotherapy, and 53 patients received hypofractionated radiotherapy. Tumour samples taken during surgery from each patient were incubated in vitro for 1 h at 37 degrees C with BrdUrd using the high pressure oxygen method. The percentage of BrdUrd-labelled cells (BrdUrd labelling index [BrdUrd LI]), and the total DNA content were evaluated:

RESULTS

The tumours showed variability in the BrdUrd LI values, which ranged from 0.3 to 19.1%. No difference was observed in mean BrdUrd LI between grade III and grade IV sub-groups. A significantly higher percentage of DNA aneuploidy was observed in grade III gliomas (69.4%) than in grade IV gliomas (52.8%). Univariate analysis showed that younger patients (< or = 51 years) (P = 0.021) with grade III gliomas (P = 0.030) and low tumour proliferation rate (BrdUrd LI < or = 2.7%, P = 0.028) had significantly higher 5-year survival rates. Tumour ploidy had no influence on patients' survival (P = 0.591). However, Cox multi-variate analysis showed that only age over 51 years, and high tumour proliferation rate (BrdUrd LI > 2.7%), were significant unfavourable prognostic factors in patient survival.

CONCLUSION

In this study, independent prognostic factors for patients with high-grade gliomas treated with surgery and post-operative radiotherapy are age and tumour proliferation rate assessed according to the BrdUrd LI.

Glioblastoma in the elderly: current and future trends

Data from a prospective trial large enough to provide a reliable analysis of outcome and prognostic factors in elderly patients with glioblastoma (GBM) are not yet available in the literature. Extensive tumor removal appears to offer patients the best possible chance of a speedy neurological recovery. Adequate radiotherapy (RT) should always be given to elderly patients if they have undergone gross total debulking and have maintained a good performance status. It is, however important to bear in mind that the risk of long-term cognitive impairment may be higher in patients on high-dose RT and that a short course of accelerated RT can achieve the same survival. Rather than being ruled out on principle, chemotherapy should be considered on the basis of an accurate assessment of the factors that might compromise the individual patient's tolerance to drugs administered. Temozolomide appears to be the best available chemotherapy in this population of patients.

Glioblastoma multiforme in the elderly: a therapeutic challenge

INTRODUCTION

Elderly patients with glioblastoma multiforme (GBM) are frequently excluded from cancer therapy trials, treated suboptimally or not treated at all. The average survival in elderly patients is 4-8 months. The goal of the present study was to evaluate the efficacy of different treatment options in terms of survival in an elderly population affected with GBM.

MATERIALS AND METHODS

About 34 Patients with primary supratentorial GBM aged 65 or higher were included in this study. All patients underwent craniotomy and tumor mass resection. After surgery they received radiation therapy, chemotherapy and radioimmunotherapy in different combinations.

RESULTS

Overall median survival was 10.5 months with one patient still alive at 35 months. Survival was longer for patients who underwent total resection instead of partial (13 months vs 4 months, P=0.006). If total en-bloc resection was used a further survival advantage was obtained (16 months for en-bloc resection, 9 months for inside-out resection, P=0.008). Where a second surgical intervention was performed median survival was 21 months (P=0.05). Survival according to adjuvant therapy has been 21 months (radiotherapy, chemotherapy, radioimmunotheraphy), 18 months (radiotherapy, chemotherapy) and 7 months (radiotherapy) (P=0.0001).

CONCLUSIONS

We think that single prognostic factor such as age should be not a reason for undertreatment.

The treatment of elderly patients with high-grade gliomas

Elderly patients with cancer are frequently excluded from cancer therapy trials, treated suboptimally, or not treated at all because of the widely held belief that elderly patients do not tolerate chemotherapy and/or radiotherapy (RT) as well as younger patients. Excluding elderly patients from conventional treatment, chemotherapy in particular, is often based on ad hoc decisions rather than on sound scientific data. Malignant gliomas are the most common primary brain tumors in adults, and the age-adjusted incidence of high-grade gliomas has increased over recent years, especially in the elderly. However, few investigators focus on the treatment of high-grade gliomas in the elderly. Data from retrospective studies and meta-analyses suggest that elderly patients with high-grade gliomas have a poorer outcome than younger patients, possibly because of the presence of comorbidity, resistance to cancer therapy, genetic aberrations, different histology, neurodegeneration, or age discrimination. The optimal treatment of elderly patients with high-grade gliomas has not been determined. Surgical debulking and postoperative RT are associated with a significant increase in survival among elderly patients who are in good clinical condition. A recent report has shown that treatment with temozolomide (Temodar [US], Temodal [international]; Schering-Plough Corporation, Kenilworth, NJ) plus RT provides a significant survival benefit compared with RT alone and a significantly improved time to progression compared with RT plus standard chemotherapy (lomustine, procarbazine, and vincristine). Further, temozolomide was well tolerated in the elderly patient population and was less toxic than standard chemotherapy. Therefore, it could be recommended that a full course of RT be followed by adjuvant temozolomide in elderly patients with good prognostic factors. Further, temozolomide alone could be considered as a treatment option for elderly patients with glioblastoma with poorer performance status and for patients who cannot tolerate RT. Results from larger prospective trials will determine the optimal role of chemotherapy, particularly temozolomide, in elderly patients with malignant gliomas.

Temozolomide as an alternative to irradiation for elderly patients with newly diagnosed malignant gliomas

BACKGROUND

The optimal treatment for elderly patients (defined as patients 70 years of age or older) with malignant gliomas (MG) remains controversial. Some physicians advocate withholding therapy following diagnosis based on the observation that elderly patients do not tolerate adjuvant radiotherapy. The availability of temozolomide (TMZ), a new alkylating agent with antiglioma efficacy, offers another potential therapeutic option for these patients. The drug can be administered orally at home with minimal morbidity.

METHODS

The authors retrospectively reviewed a cohort of 86 consecutive elderly MG patients from three institutions, 32 of whom received monthly TMZ in lieu of radiation.

RESULTS

Initial Karnofsky performance score was the only predictor of survival in this cohort. No difference in survival was noted between these two groups. Toxicity was minimal in the chemotherapy-treated group and a higher percentage of patients receiving chemotherapy died at home.

CONCLUSIONS

The authors concluded that TMZ is as effective as irradiation as a treatment of elderly patients with MG. It is an alternative and, perhaps, a superior therapeutic option to irradiation, based on its ease of administration and low morbidity.

Clinical trial participation among patients enrolled in the Glioma Outcomes Project

BACKGROUND

Patient participation in well-designed and conducted clinical trials enables researchers to test new therapies. An understanding of the variables that possibly influence patient enrollment may help in patient recruitment for future trials. The authors evaluated factors that influenced patient enrollment in clinical trials using a prospective, large, multi-institutional registry of patients with malignant glioma.

METHODS

Data were examined from 708 patients who underwent first or second surgery for a malignant glioma who were enrolled in the Glioma Outcomes Project, which is a prospective observational data base that captures clinical practice patterns. The frequency of clinical trial participation and the variables that may have been associated with trial participation were evaluated. These variables included age, gender, race, household income, educational level, first versus second craniotomy, histology, and whether the patient was treated at an academic institution.

RESULTS

One hundred fifty-one of 708 patients (21.3%) participated in a clinical trial, which was higher than the participation reported typically for patients with other types of primary malignancies. In univariate analysis, race, histology, and first craniotomy were significant between the two groups, with Caucasian patients and patients with glioblastoma histology showing higher participation rates. In a multivariate logistic regression model, significant predictors included young age and glioblastoma multiforme histology.

CONCLUSIONS

The authors present information on factors that may influence clinical trial participation among patients with malignant glioma and compare their data with information described previously on patients with other types of malignant disease. The percent of participation among the patients in the current study was greater than among patients with other primary tumor sites. Strategies should be implemented to improve recruitment to neuro-oncology trials, especially in elderly and minority populations.

Age and radiation response in glioblastoma multiforme

OBJECTIVE

Advanced age is a strong predictor of shorter survival in patients with glioblastoma multiforme (GM), especially for those who receive multimodality treatment. Radiographically assessed tumor response to external beam radiation therapy is an important prognostic factor in GM. We hypothesized that older GM patients might have more radioresistant tumors.

METHODS

We studied radiographically assessed response to external beam radiation treatment (five-level scale) in relation to age and other prognostic factors in a cohort of 301 GM patients treated on two prospective clinical protocols. A total of 223 patients (74%) were assessable for radiographically assessed radiation response. A proportional odds ordinal regression model was used for univariate and multivariate analysis.

RESULTS

Younger age (P = 0.006), higher Karnofsky Performance Scale score before radiotherapy (P = 0.027), and more extensive surgical resection (P = 0.028) predicted better radiation response in univariate analyses. Results were similar when clinical criteria were used to classify an additional 61 patients without radiographically assessed radiation response (stable versus progressive disease). In multivariate analyses, age and extent of resection were significant independent predictors of radiation response (P < 0.05); Karnofsky Performance Scale score was of borderline significance (P = 0.07).

CONCLUSION

Older GM patients are less likely to have good responses to postoperative external beam radiation therapy. Karnofsky Performance Scale score before radiation treatment and extent of surgical resection are additional predictors of radiographically assessed radiation response in GM.

Brain tumors in the older person

BACKGROUND

The incidence of brain tumors is increasing rapidly, particularly in the older population. Advances in molecular biology help to explain differences in biologic behavior and response to therapy of brain tumors in the elderly compared with younger patients. The number of elderly patients who desire and receive therapy for brain tumors and are included in clinical trials is increasing.

METHODS

This article reviews the literature on the epidemiology, clinical aspects, and therapy of brain tumors, with emphasis on the older patient population.

RESULTS

The increased incidence of brain tumors in the elderly is principally due to the increasing number of people who comprise the older population. Age and performance status are important independent prognostic indicators, together with tumor histology. Surgery, radiation therapy, and chemotherapy can benefit elderly patients with brain tumors with favorable histologies, tumor location, and good performance status. The response rates to available therapies are less favorable than in younger patients, and only a small number of elderly patients are enrolled in clinical studies addressing new treatment modalities.

CONCLUSIONS

Brain tumors in the elderly have specific characteristics that determine their biologic behavior and response to therapy. There is a need for clinical studies designed for treatment of brain tumors in older patients, and requirements for rehabilitation and support systems for the elderly need to be addressed.

Outcomes and prognostic factors in recurrent glioma patients enrolled onto phase II clinical trials

PURPOSE

To determine aggregate outcomes and prognostic covariates in patients with recurrent glioma enrolled onto phase II chemotherapy trials.

PATIENTS AND METHODS

Patients from eight consecutive phase II trials included 225 with recurrent glioblastoma multiforme (GBM) and 150 with recurrent anaplastic astrocytoma (AA). Their median age was 45 years (range, 15 to 82 years) and their median Karnofsky performance score was 80 (range, 60 to 100). Prognostic covariates were analyzed with respect to tumor response, progression-free survival (PFS), and overall survival (OS) by multivariate logistic and Cox proportional hazards regression analyses.

RESULTS

Overall, 34 (9%) had complete or partial response, whereas 80 (21%) were alive and progression-free at 6 months (APF6). The median PFS was 10 weeks and median OS was 30 weeks. Histology was a robust prognostic factor across all outcomes. GBM patients had significantly poorer outcomes than AA patients. The APF6 proportion was 15% for GBM and 31% for AA, whereas the median PFS was 9 weeks for GBM and 13 weeks for AA. Results were also significantly poorer for patients with more than two prior surgeries or chemotherapy regimens.

CONCLUSION

Histology is a dominant factor in determining outcome in patients with recurrent glioma enrolled onto phase II trials. Future trials should be designed with separate histology strata.

Outcome in elderly patients undergoing definitive surgery and radiation therapy for supratentorial glioblastoma multiforme at a tertiary care institution

PURPOSE

To determine the efficacy of definitive surgery and radiation in patients aged 70 years and older with supratentorial glioblastoma multiforme.

METHODS AND MATERIALS

We selected elderly patients (> or = 70 years) who had primary treatment for glioblastoma multiforme at our tertiary care institution from 1977 through 1996. The study group (n = 102) included 58 patients treated with definitive radiation, 19 treated with palliative radiation, and 25 who received no radiation. To compare our results with published findings, we grouped our patients according to the applicable prognostic categories developed by the Radiation Therapy Oncology Group (RTOG): RTOG group IV (n = 6), V (n = 70), and VI (n = 26). Patients were retrospectively assigned to prognostic group IV, V, or VI based on age, performance status, extent of surgery, mental status, neurologic function, and radiation dose. Treatment included surgical resection and radiation (n = 49), biopsy alone (n = 25), and biopsy followed by radiation (n = 28). Patients were also stratified according to whether they were optimally treated (gross total or subtotal resection with postoperative definitive radiation) or suboptimally treated (biopsy, biopsy + radiation, surgery alone, or surgery + palliative radiation). Patients were considered to have a favorable prognosis (n = 39) if they were optimally treated and had a Karnofsky Performance Status (KPS) score of at least 70.

RESULTS

The median survival for patients according to RTOG groups IV, V, and VI was 9.2, 6.6, and 3.1 months, respectively (log-rank, p < 0.0004). The median overall survival was 5.3 months. The definitive radiation group (n = 58) had a median survival of 7.3 months compared to 4.5 months in the palliative radiation group (n = 19) and 1.2 months in the biopsy-alone group (p < 0.0001). Optimally treated patients had a median survival of 7.4 months compared to 2.4 months in those suboptimally treated (p < 0.0001). The favorable prognosis group had an 8.4-month median survival compared to 2.4 months in the unfavorable group (p < 0.0001). On multivariate analysis, the KPS, RTOG group, favorable/unfavorable prognosis, and optimal treatment/suboptimal treatment were significant predictors of survival.

CONCLUSION

Elderly patients with good performance status (> or = 70 KPS) when treated aggressively with maximal resection and definitive radiation had longer survival than those treated with palliative radiation and biopsy. Aggressive treatment in such patients should be considered.

Long-term survival in a patient with supratentorial glioblastoma: clinical considerations

Glioblastoma, a malignant tumor of neuroepithelial origin, is relatively uncommon in childhood, during which it accounts for 7%-9% of brain tumors. A few patients (about 3%) live more than 5 years. We report a 13-year-old girl who was admitted because one month earlier she had begun to present headache and diplopia. Brain computed tomography (CT) showed a right frontal tumor. At operation, complete excision of the visible tumor was performed. Histologic examination showed that the tumor was a glioblastoma multiforme. The patient underwent 52 Gy of external beam radiotherapy to the enhancing tumor mass plus 3-cm border, and chemotherapy with nitrosourea (BCNU). Fourteen years, 9 months later, the patient presents neither neurological deficits nor radiological relapse. We confirm that younger age, the one immutable prognostic factor, supports a particularly aggressive approach to the treatment of glioblastomas.

Prognostic factors in low-grade supratentorial astrocytomas: a uni-multivariate statistical analysis in 76 surgically treated adult patients

A retrospective uni-multivariate statistical analysis was performed on 32 prognostic factors to investigate their importance in predicting survival in a series of 76 adult patients with low-grade supratentorial astrocytomas treated over a 13-year period. The end point used for this study was the length of survival. The median survival time was 40 months. Overall actuarial survival at 2, 5, and 10 years was 69%, 38%, and 22%, respectively. Radical resection of the neoformation, a higher preoperative Karnofsky performance status (KPS) score, and an age younger than 50 years are strongly correlated with survival; postoperative radiotherapy appears to be associated with increased survival only in patients under 50 years of age.

Survival in malignant astrocytoma at King Khalid University Hospital

Malignant astrocytoma (Kernohan grade III and IV) still has one of the worst outcomes of all malignant tumors. To determine factors affecting the survival of patients with malignant astrocytoma in Saudi Arabia, a retrospective study of 76 cases that were treated at King Khalid University Hospital over one decade was carried out. Kaplan-Meier survival diagrams were constructed for each prognostic factor. Twenty-eight percent of cases survived two years. A significantly better survival rate was found in females, patients </=50 years and patients who had re-operation for a recurrence. A better survival rate which did not reach significance was found in patients with grade III tumors, patients with a Karnofsky score of >/=70 at presentation, patients who had craniotomy and excision and patients who had radiotherapy. It is suggested that to improve the outcome of patients with malignant astrocytoma, aggressive surgical excision with radiotherapy (and possibly chemotherapy) is required.

Heterogeneity in response to treatment with buthionine sulfoximine or interferon in human malignant glioma cells

Two tumor cell lines were established from each of three human malignant glioma biopsy specimens (M059, M067, M071) and sensitivity to treatment with radiation or chemotherapeutic agents (BCNU, nitrogen mustard) was determined. The effects of recombinant human interferon-alpha (rIFN) on the radiation response and of buthionine sulfoximine (BSO) on the drug response were investigated as well. For tumor M059, two cell lines that differed significantly in radiosensitivity were isolated (surviving fractions at 2 Gy = 0.02 and 0.64). The chemosensitivity and response to chemical modification differed as well. Cell lines established from tumor M071 differed in their response to rIFN only and were not sensitized by BSO. M067 cell lines showed little difference and were not sensitized by either agent. These results suggest that differences may exist both within and among human malignant gliomas with regard to their sensitivity to drugs, radiation, and the ability of chemical agents to modify treatment responses.

Glutathione levels and chemosensitizing effects of buthionine sulfoximine in human malignant glioma cells

Biopsy samples and cultured cells derived from them were obtained from 39 patients with malignant glioma and were analyzed for 1) glutathione (GSH) content; 2) sensitivity to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and/or nitrogen mustard (HN2) treatment and 3) the effect of buthionine sulfoximine (BSO) treatment on BCNU and/or HN2 cytotoxicity. The average GSH concentration of biopsy specimens was lower than those of cultured cells (2.36 +/- 0.44 vs. 11.42 +/- 2.32 nmol/10(6) cells). While some of the tumor specimens were sensitive to either BCNU or HN2, the majority were resistant to both. However, 8 of 23 tumors tested showed enhanced sensitivity to BCNU following treatment with BSO. Five of 17 tumors were similarly sensitized to HN2 by BSO. These results suggest that BSO chemosensitization may be of value for certain patients and that screening assays may help identify treatment-sensitive individuals.