PEDIATRIC BRAIN TUMORS
Co-Chairs: Roger Packer, M.D., and Ian Pollack, M.D.
Participants:
Francis Ali-Osman
David Ashley
Jaclyn A. Biegel
James Boyette
Greta Bunin
Tom Curran
Henry Friedman
James Goldman
Alison Hannah
Mark A. Israel |
C. David James
David Kaplan
Kenneth A. Krohn
Larry Kun
Frederick F. Lang
Marla B. Luskin
Lorraine Marin
Robert H. Miller
Sherie Morrison
Raymond Mulhern |
Sarah Nelson
Judith J. Ochs
Scott Pomeroy
Sam D. Rabkin
Richard Ransohoff
Lucy B. Rorke
Bruce Rosen
David H. Rowitch
James Rutka
Gail Segal |
Dennis C. Shrieve
Malcolm Smith
Evan Snyder
Diane Traynor
Richard Vallee
Jeanne Young
Susan L. Weiner
Daphne A. Haas-Kogen |
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STATEMENT OF THE PROBLEM
Childhood brain tumors are the second most frequent malignancy of childhood
and the most common form of solid tumor. Tumors of the central nervous
system (CNS) comprise 22% of all malignancies occurring among children
up to 14 years of age and 10% of tumors occurring among 15–19-year-olds.
Although rapid progress has been made in the treatment of some forms of
childhood cancer, such as acute lymphatic leukemia, the outcome for children
with primary CNS tumors has remained poor and for most tumors has not changed
over the past decade. Brain tumors are now the leading cause of death from
childhood cancer, accounting for 24% of cancer-related deaths in 1997 among
persons up to 19 years of age. In addition, due to either the effects of
the tumor or the treatment required to control it, survivors of childhood
brain tumors often have severe neurologic, neurocognitive, and psychosocial
sequelae.
Tumors in childhood differ significantly from adult lesions in their
sites of origin, histological features, clinical presentations, and proclivity
to disseminate throughout the nervous system early in the course of illness.
Whereas 90% of adult tumors arise in the cerebral cortex, 50% of childhood
brain tumors originate infratentorially, in the cerebellum, brain stem,
or fourth ventricular region. A large proportion of brain tumors in adults
are the result of metastatic lesions from nonprimary brain sites, and the
primary tumors are for the most part glial tumors and meningiomas. In contrast,
childhood brain tumors mainly represent primary CNS lesions and, although
gliomas make up the majority of childhood neoplasms, other tumor type,s
such as medulloblastomas, primitive neuroectodermal tumors, pineoblastomas,
atypical teratoid tumors, and other embryonal neoplasms, contribute a significant
proportion.
The biological behavior and management of childhood tumors depends on
not only the histological character of the tumor but also its location
within the nervous system. For example, childhood low-grade cerebellar
gliomas may be curable in over 90% of patients with surgery alone, whereas
brain stem gliomas (even if "low-grade") carry the dismal prognosis of
death for most child patients within 18 months of diagnosis. The aspects
of tumor dissemination are extremely important for childhood brain tumors.
Control of local disease remains problematic for many forms of childhood
brain tumors; however, specific types of tumors, especially embryonal tumors,
have a high proclivity for early dissemination within the nervous system
and treatment approaches must take into account this tendency for early
tumor spread. The neurobiological underpinnings of these differences are
largely unknown: the importance of the relationship between tumor type
and location is poorly studied; the reasons why tumors primarily arise
at certain ages and have proclivity to specific areas of brain are unclear;
and the ways to utilize these differences to alter management and improve
outcome require further investigation.
The histological heterogeneity of childhood brain tumors makes it necessary
to develop separate lines of investigation into the molecular mechanisms
of each type of tumor, the effect of the surrounding milieu on the tumor,
and the development of effective treatment approaches. A variety of different
classification systems have been utilized for childhood brain tumors, and
controversy still exists concerning the most appropriate nomenclature for
some tumors. The classification systems in use are still based on relatively
subjective criteria, making comparison across different studies difficult.
Although some subtypes of childhood brain tumors are relatively rare, such
as primitive neuroectodermal tumors (excluding medulloblastoma), atypical
teratoid tumors, medulloepitheliomas, dysembryoplastic neuroepithelial
tumors, desmoplastic infantile gangliogliomas, and superficial cerebral
astrocytomas of infancy, together they constitute a significant percentage
of childhood brain tumors and a major cause of morbidity and mortality.
Studies focusing on the more frequent adult and pediatric CNS tumors often
do not include such rare tumors, which results in missed opportunities
to understand these tumors’ biology and create more effective treatment
regimens.
Even within the tumor types commonly found in both children and adults,
studies focusing on tumors occurring in adults may not result in new insights
for pediatric tumors. The molecular aspects of glial neoplasia in children,
for example, appear to differ substantially from those in adults. Most
childhood low-grade gliomas are pilocytic astrocytomas, whereas this tumor
type is relatively infrequent in adults. Pilocytic astrocytomas have a
different biology than fibrillary or other grade 2 lesions. For example,
one major difference is that pilocytic astrocytomas rarely mutate into
higher-grade lesions, whereas fibrillary astrocytomas often do so. Furthermore,
even fibrillary low-grade gliomas in childhood rarely mutate into higher-grade
tumors in the childhood years, despite this common occurrence in adults.
For progress to be made in this subset of tumors, research must be focused
directly on pediatric low-grade gliomas.
The differences between the neurobiological features of glial neoplasia
in children and those of the disease in adults are not limited to low-grade
tumors. Approximately 40% of grade IV gliomas in adults exhibit amplification
of epidermal growth factor receptor, whereas this change is less commonly
detected in childhood glioblastomas. In addition, P53 mutations, which
are observed in 50% of grade III and grade IV gliomas in adults, are rarely
seen in high-grade gliomas in children. These differences may at least
partly account for the somewhat better prognosis for childhood high-grade
gliomas; a subset of children with high-grade glial tumors, including glioblastoma
multiforme (as high as 20% in some studies), survive after treatment. In
addition, evidence from randomized prospective studies shows that long-term
survival for childhood glioblastoma multiforme is improved by the addition
of chemotherapy to radiotherapy; such data are lacking in adults.
A focused effort to define relevant molecular markers for prognosis
in childhood glial tumors may facilitate improved diagnostic and therapeutic
stratification of patients and more appropriate treatment. Treatment strategies
may also need to differ for childhood and adult high-grade gliomas. Also
needed are innovative classification systems that integrate molecular,
neurobiological, and neuroimaging aspects with histological diagnosis to
develop more clinically relevant nomenclatures for these tumors; this will
guide epidemiological research, biological studies, and treatment approaches.
The molecular pathways involved in the development of primitive neuroectodermal
tumors are just being unraveled. Research focused on the glial tumors that
predominate in adults may not lead to a better understanding of these primitive
embryonal tumors. Although such tumors are not unique to childhood, they
are substantially more common in children than in adults. There has been
significant controversy over the most appropriate classification of childhood
primitive neuroectodermal tumors, primarily whether all such tumors should
be grouped into one category or better subdivided based purely on tumor
location. Recent studies have suggested, although not proven, that although
these tumors share histological similarities, molecular features of the
lesions occurring outside the posterior fossa are distinct from those arising
in the posterior fossa. In addition, studies have recently shown that other
molecular features, such as TrkC expression, correlate with outcome in
medulloblastoma and may lead to better stratification systems. Other neurobiological
abnormalities have been noted in these primitive neuroectodermal tumors,
and research into the molecular pathways involved in tumor development
and growth is needed.
Infants and very young children with primary CNS tumors often harbor
lesions that are apparently unique to the early childhood years. Some of
these tumors, such as atypical teratoid tumors and medulloepithelioma,
although rare, are a significant problem in the pediatric age range. More
global investigations into brain tumors, especially research focusing on
more common adult tumors, will fail to address these important lesions.
Many of these embryonal tumors are apparently true congenital tumors, and
studies of the mechanism of their development may also lead to important
insights into general brain development. Similarly, studies of brain development
may lead to insights into the neurobiological aspects of these and other
embryonal tumors.
Also related to age are the effects of therapy on the developing nervous
system. As stated previously, some childhood brain tumors are true congenital
lesions, whereas others, such as medulloblastoma and ependymoma, peak in
incidence before age 5 years. Given the proclivity of primitive tumors
to disseminate within the nervous system early in the course of disease,
treatment approaches must focus on controlling not only local disease but
also disease in all sites of the nervous system. This often requires treatment
to be aimed at the entire nervous system in the young child and heightens
the likelihood of treatment-related brain injury.
The long-term effects of the tumor and its treatment on outcome are
extremely important issues in both children and adults with brain tumors,
but because of the above-mentioned reasons, they take on even more significance
in childhood. It has been well documented that young children with brain
tumors, independent of the form of treatment they receive, have significant
neurological and cognitive sequelae. Furthermore, for older children and
adolescents, treatment may result in permanent long-term sequelae, especially
neurocognitive difficulties. Other common sequelae include endocrinological
dysfunction, focal neurological deficits, and psychosocial sequelae.
In a recent retrospective questionnaire review of 1,845 children with
brain tumors who survived for at least 5 years, it was noted that seizures,
convulsions, or blackouts occurred in 28% of survivors; headaches, including
migraines, were a problem in 37% of patients; and motor disabilities, such
as balance problems, weakness of the arms of legs, or tremors, were noted
in over 50% of children. A sizeable minority of patients had blindness
in one or both eyes, double vision, hearing loss, or persistent tinnitus.
Over 50% of those surviving for 5 years from the date of diagnosis of their
childhood brain tumors required special education or learning-disabled
classroom settings, including 70% of those less than 3 years of age and
62% of those between 3 and 9 years of age. The incidence of secondary brain
tumors in long-term survivors of childhood brain tumors is rising, and
second malignancies are almost always fatal for this patient population.
These sobering numbers highlight the problems faced by survivors of childhood
brain tumors and the need for further research into means to reduce long-term
sequelae and remediate such problems when they arise.
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CHALLENGES AND QUESTIONS
On the largest scale, the overriding challenge for research into pediatric
brain tumors is to improve outcome for children with a host of different
types of brain tumors. The predominant barriers are the relative infrequency
of any individual tumor type, the presence of embryonal/primitive tumors
that often disseminate to the leptomeninges, and the lack of interest in,
focus on, and funding for research on these primitive tumors. Specific
challenges associated with improving outcomes for children with pediatric
brain tumors and barriers to meeting these challenges are grouped below
into four categories: Tumor Biology, Epidemiology, Treatment, and Long-Term
Sequelae.
Tumor Biology
Challenges
- Improved understanding of the genetic and environmental factors
involved in the development of childhood CNS tumors
- Increased understanding of the cellular origin of different types of
PEDIATRIC BRAIN TUMORS
- Greater insight into the relationship between normal brain development
and the neurogenetic/biologic underpinnings of childhood nervous system
tumors
- Determination of factors responsible for the proclivity of some childhood
brain tumors to disseminate within the nervous system early in the course
of illness
- Clarification of the relationship between age, development, and outcome
of childhood brain tumors
- Enhanced understanding of the biologic differences between childhood
and adult gliomas and the development of treatment approaches that take
advantage of such differences
- Better understanding of the neurobiology of childhood primitive neuroectodermal
tumors (including medulloblastoma) and other less common embryonal tumors
- Development of better animal models that mimic human pediatric brain
tumors, including those primarily occurring in children, such as PNETs
and other rarer pediatric tumors (e.g., atypical teratoid tumors)
- Definition of relevant molecular markers for the prognosis of the
diverse forms of childhood brain tumors
Barriers
- Insufficient appreciation of the important distinction between research
required for childhood brain tumors and research required for adult tumors
- Lack of emphasis placed on the defining biologic differences between
histologically identical tumors occurring in children and adults, especially
the low- and high-grade gliomas
- Paucity of investigations focused on the molecular, genetic, and biologic
aspects of embryonal childhood brain tumors, including primitive neuroectodermal
tumors
- Lack of understanding of the relationship between normal brain development
and aberrations of such development in the etiology of childhood brain
tumors
- Lack of understanding of the uniqueness of the rarer childhood brain
tumors; their overall importance, in total; and the need to study these
types of neoplasms individually
- Lack of usable surrogate markers to determine the prognosis of childhood
brain tumors and to evaluate the potential efficacy of agents used to treat
such tumors
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Epidemiology
Challenges
- Creation of a biologically-based classification of childhood brain
tumors that integrates molecular aspects, neurobiological parameters and
other neurodiagnostic findings
- Determination of the incidence of individual types of childhood brain
tumors, including low grade neoplasms, congenital tumors, and embryonal
neoplasms
Barriers
- Variability in the classification of rare childhood brain tumors,
especially congenital and embryonal lesions
- Lack of methods to study individual tumor types that occur less commonly
- New coding of low-grade gliomas as "benign" tumors, which could increase
the likelihood that children with these diagnoses will not be included
in cancer registries
- Lack of funding for epidemiological research, especially for the less
common, but critically important, childhood brain tumor subtypes
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Treatment
Challenges
- Development of more effective treatments for childhood low- and
high-grade gliomas
- Development of more effective and safer treatment approaches for childhood
embryonal and primitive tumors
- Development of immunotherapeutic approaches aimed at improving control
of localized and disseminated pediatric brain tumor disease
- Development of new, safer approaches to control CNS disseminated disease
- Development of innovative biologically-based treatments for childhood
brain tumors
Barriers
- Reluctance of industry to focus on developing drugs for pediatric
brain tumors because of the relative rarity of childhood brain tumors
- Difficulty in performing clinical trials for specific brain tumor
subtypes because of the relative infrequency of specific types of childhood
brain tumors
- Insufficient development of novel therapeutics designed for childhood
brain tumors such as primitive neuroectodermal tumors
- Hesitancy to apply new therapies early in their development, especially
biologically-based treatments, to childhood brain tumors
- Paucity of research into the impact of new neurobiological treatments,
such as anti-growth factor agents and anti-angiogenesis agents, on the
developing nervous system
- Limited scope of research focused on the immunocompetence of children
with brain tumors and the potential utility of different immunotherapeutic
approaches for children with brain tumors
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Long-Term Sequelae
Challenges
- Detection of long-term neurologic, cognitive, endocrinologic, systemic
and psychosocial sequelae of childhood brain tumors and their treatments,
and determination of the incidence of these sequelae
- Investigation into factors that are involved in the development of
neurotoxicity and host neurobiological/genetic characteristics that underlie
the variable severity of neurologic compromise in an individual child
- Development of new strategies to prevent, ameliorate and remediate
neurocognitive and psychosocial sequelae of childhood brain tumors and
their treatment
- Evaluation of the impact of innovative biologically-based therapies
on the developing nervous system
- Research into factors involved in the development of secondary tumors
in long-term survivors of PEDIATRIC BRAIN TUMORS and more effective means
to treat such secondary malignancies.
- Research into the effects of the diagnosis of a brain tumor on the
family unit, especially parental relationships and the impact on other
children in the family
Barriers
- Lack of appreciation of the severe long-term sequelae suffered by
children who have brain tumors, either due to their tumor or its treatment
- Lack of emphasis on the psychosocial sequelae of these tumors on the
child and the family
- Lack of information concerning the development and treatment of second
malignancies in childhood brain tumor survivors
- Lack of neuro-investigative techniques which take into account the
developing nervous system and the differences required in evaluation between
adults and children
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RESEARCH AND SCIENTIFIC PRIORITIES
Priority 1: Understand the signaling systems involved in mitogenesis,
survival, and cell death for pediatric tumors.
- Understand how these signaling systems relate to those in developmental
neurobiology
- Use this understanding to identify new targets for pediatric brain
tumor therapy.
Priority 2: Fully characterize the phenotypic and genetic alterations
that are unique to benign and malignant PEDIATRIC BRAIN TUMORS.
- Develop novel in vitro and animal models that faithfully recapitulate
the biology of these tumors.
- Use these models for the identification and prioritization of targeted
therapeutic strategies for PEDIATRIC BRAIN TUMORS.
Priority 3: Investigate in detail the impact of the tumor and its treatment
on long-term neurological, cognitive, and psychological functional outcome,
and develop new means to prevent, ameliorate, and remediate such dysfunction.
Priority 4: Conduct pediatric clinical trials of novel therapeutic
agents at an appropriately early stage in their development; include in
these trials comprehensive and noninvasive assessments (including innovative
imaging and biological studies) of the short- and long-term effects of
such agents on the child and on the developing nervous system.
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RESOURCES NEEDED
- Tumor banking of pediatric brain tumor tissues
- DNA microarrays applicable to PEDIATRIC BRAIN TUMORS and nervous system
development
- Tissue arrays for pediatric CNS tumors
- Development of in vitro model systems for PEDIATRIC BRAIN TUMORS
- Animal model systems for PEDIATRIC BRAIN TUMORS
- Greater availability of well-characterized and validated clones or
lines of stem cells
- Imaging techniques for identifying tumors in situ for animal models
of pediatric tumors
- Coordinated effort, on a national basis, of core facilities or coordinated
individual laboratories with specific expertise and models (both academic
and private industry) to facilitate the development of new drugs, biological
agents, or other treatment approaches
- Funding for neuropsychological testing
- Validated, user-friendly, pediatric instrument for measuring quality
of life
- Development of neuroimaging techniques that correlate with subclinical
and clinical neurotoxicity.
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