Annual Forum 1990 – Molecular Origins of Pediatric Embryonal Malignancies

Mark A. Israel, MD, University of California, San Francisco, CA

June L. Bieder, Ph.D., Memorial Sloan-Kettering Cancer Center, New York, NY
Beverly S. Emanuel, Ph.D., Children’s Hospital of Philadelphia, Philadelphia, PA
Ed Harlow, Ph.D., Massachusetts General Hospital Cancer Center, Charlestown, MA
Mark A. Israel, MD, University of California, San Francisco, CA
Michael P. Kriegler, Ph.D., Cetus Corporation, Emeryville, CA
John J. Mulvihill, MD, University of Pittsburgh, Pittsburgh, PA
Eric N. Olson, Ph.D., MD Anderson Cancer Center, Houston TX
Sven Pahlman, MD, University of Uppsala, Uppsala, Sweden
Bernd R. Seizinger, MD, Ph.D., Massachusetts General Hospital, Boston, MA
George Vande Woude, MD, NCI-Frederick Research and Development Facility, Frederick, MD
Bernard E. Weissman, MD, University of North Carolina, Chapel Hill, NC

Layout and Goals

  1. Cancer as a Genetic Disorder
  2. Biologic Basis of Embryonal Malignancies: Disordered Differentiation
  3. Somatic Mutation as an Oncologic Mechanism
  4. Molecular Mechanisms of Oncologic Import

A group of internationally respected investigators convened on Hilton Head Island from 15 to 17 November, 1990 to focus on the Molecular Origins of Pediatric Embryonal Malignancies, the topic of the VIth Annual William Guy Forbeck Research Foundation “Think Tank Forum.” The goal of this unique forum was twofold – to identify the most recent advances in our understanding of the genetic basis of pediatric malignancies and to evaluate findings that might offer new opportunities for the development of new diagnostic or therapeutic targets.

During the past decade, novel approaches to cancer research have emerged that are providing important insights into the molecules involved in the conversion of a normal cell to a malignant one. Particularly important have been the dramatic advances in cell biology and recombinant DNA technology that have focused attention on cancer as a genetic disorder. The identification of specific genetic alterations that seem to be related intimately to malignancy has been of pivotal importance and has opened new lines of investigation, elucidating the biochemical pathways that mediate the development of cancer and its clinical features. There is now widespread recognition that the biologic alterations indicative of malignancy are closely related to events integral to the formation of complex organisms. Coordinated growth regulation, differentiation, the development of complex tissues, and cell migration are now under intense scrutiny and cancer is emerging as a disorder of these normal physiologic events. Within this framework, it should be possible to reconcile many of the diverse laboratory and clinical observations that have led to cancer’s being considered among the most enigmatic of diseases.

Discussions during this forum provided an opportunity for outstanding investigators working on different pediatric tumors and different cellular mechanisms of growth control to interact and share both their most recent findings as well as details of their experimental approach. Without doubt, there was a vigorous and highly productive exchange of scientific ideas.

Outcome Report
Pediatric embryonal tumors were the first malignancies in which a response to chemotherapy was recognized and they have since been important clinical models in developing many principles of cancer treatment. The molecular origins of embryonal tumors were the focus on the 1990 Forbeck Forum, where laboratory researchers and clinical oncologists met to exchange ideas about the regulation of cell differentiation and growth and its disruption on childhood cancer. 

The forum first addressed childhood cancer as a genetic disorder. A chain of sequential genetic events may lead to the development of embryonal tumors and contribute to their highly malignant behavior. Wilms tumor, for example, may develop in a child whose kidneys failed to differentiate and mature normally during embryonic development. Neuroblastoma and retinoblastoma may develop similarly. Within this context, the forum then focused on molecular studies, emphasizing the role of tumor suppressor genes in the development of childhood tumors. Malignant (cancerous) changes in cells at the molecular level are often associated with the loss of genetic material, which appears to be a sensitive indictor of the site of tumor suppressor genes on a chromosome, the structure in the cell’s nucleus that carries the genes. The loss of genetic material from tumor cell chromosomes appears to have great importance in the development of cancer.

Childhood tumors seem to be genetically distinct from the corresponding tumors in adults. Possible one third of all childhood embryonal brain tumors have an alteration and loss of DNA sequences from chromosome 17. This particular structural anomaly has been seen in only one of over 100 adult gliomas studies. In adult gliomas that have lost chromosome 17 DNA sequences the loss may be related to the abnormalities of the p53 gene, but preliminary studies of p53 in several pediatric gliomas did not show the mutations in this gene. Rather, it seems that a different gene on the short arm of chromosome 17 distal to p53 might be involved.

The functional role of proteins encoded by tumor suppressor genes was discussed extensively. At least three types of such genes have been defined: 1. Genes that control the growth rate of life span of cells under experimental conditions; 2. Genes that control tumorigenic potential of individual cells; 3. Genes that regulate normal cellular differentiation. Provocative biochemical studies of growth suppression by tumor suppressor genes have shown molecular interactions that suggest a link between those genes and cell cycle regulatory mechanisms, but the significance of those interactions is still unclear. Other genes are known to contribute to tumor development by stimulating cell growth. Among these oncogenes, mos is one of the best understood. It has been shown for the first time that the normal counterpart of the mos gene functions during a critical phase of the cell cycle, suggesting that the transforming ability of mos stem from the inappropriate activation of cell cycle division at a time when cellular growth should be arrested.

In other work, research findings emphasize that successful treatment depends not only on the choice of therapy, but also on the biologic characteristics of the tumor and, presumably, the patient. While most of the body’s natural defenses against cancer cells are not well understood, it appears that some naturally occurring substances either can modify the biologic behavior of tumor cells or are tumoricidal. In planned clinical studies, tumor infiltrating cells (TILs) are genetically altered in the laboratory by the addition of a gene encoding necrosis factor (TNF) to yield TNF-producing cells that can specifically target tumor cells. These cells will then be used in treating cancer patients to produce high local concentrations of TNF. This new site-directed therapy should permit clinicians to lower severely toxic systemically administered doses of TNF.

The different but distinctly related lines of investigation discussed during the 1990 Forbeck Forum on Molecular Origins of Pediatric Embryonal Tumors provided important insights into the molecular events that initiate and mediate the oncogenic process. It appears that pediatric embryonal tumors again will serve as important models in designing novel approaches to cancer treatment.