2 2 8 Abstracts "21 NON-RANDOM CHROMOSOMAL CHANGES IN CNS PRIMITIVE NEUROECTODERMAL TUMORS/MEDULLOBLASTOMA (PNET-MB) Jaclyn A. Biegel, Roger J. Packer, Lucy B. Rorke, and Beverly S. Emanuel, The Children's Hospital of Philadelphia, Philadelphia, PA We have prepared karyotypes from 20 PNET-MB in pediatric patients ranging in age from 6 months to 16 years. Nineteen cases were newly diagnosed primary posterior fossa tumors° One case was a recurrent tumor in a patient previously treated with radiation. Cytogenetic results were obtained from direct preparations and/or short term (1-10 days) culture. Four tumors were near tetraploid, and 16 were near diploid. Three tumors had apparently normal karyotypes Seventeen tumors demonstrated numerical changes, deletions, and/or non-reciprocal translocations. Two tumors contained double minutes. In at least two tumors, structural abnormalities were noted for chromosomes 1,5,7,9,11 or 17. The most consistent change was an i(17q), present in 5 cases. Strikingly, in 3 of these 6 tumors, the i(17q) was the only structural abnormality observed. Tumor specific loss of a sex chromosome was the only other change noted. An i(17q) is not specific for pediatric PNET-MB, since it is also seen in myeloid leukemias and other solid tumors. However, it may be a primary change related to tumor development and/or progression of PNET-MB. Clinically, there was no correlation between cytogenetics and pathology of the tumors, size of the tumor, extent of metastasis or surgical resection. All of the patients are alive to date, however longer follow-up times may reveal differences amongst these patients that correlate the cytogenetic findings with prognosis. *22 SEARCH FOR A NEW KIND OF ANTIONCOGENE ON HUMAN CHROMOSOME 22q. - FACTS AND FANCIES. K.D.ZANG and N. BLIN, Institute of Human Genetics, University of Saarland, 665~ Homburg, W.Germany. Loss of chromosome 22(q) is a typical event in the majority of meningiomas and is a non-random event in several other tumors, frequently existing as a mosaic condition. This finding led to the assumption of a hypothetical regulatory gene whose (heterozygous) loss could induce unlimited cell proliferation. - Recent molecular studies confirm the loss of genes on 22q in those tumors. In contrast to the RB locus present data do not prove, however, the homozygous loss of any sequence on 22q of the tumors in question. So both a recessive and an intermediate, an independent and an interactive antloncogene action might be possible.

Non-random chromosomal changes in CNS primitive neuroectodermal tumors/medulloblastoma (PNET-MB)

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Page 1: Non-random chromosomal changes in CNS primitive neuroectodermal tumors/medulloblastoma (PNET-MB)

2 2 8 Abstracts

"21 NON-RANDOM CHROMOSOMAL CHANGES IN CNS PRIMITIVE NEUROECTODERMAL TUMORS/MEDULLOBLASTOMA (PNET-MB)

Jaclyn A. Biegel, Roger J. Packer, Lucy B. Rorke, and Beverly S. Emanuel, The Children's Hospital of Philadelphia, Philadelphia, PA

We have prepared karyotypes from 20 PNET-MB in pediatric patients ranging in age from 6 months to 16 years. Nineteen cases were newly diagnosed primary posterior fossa tumors° One case was a recurrent tumor in a patient previously treated with radiation. Cytogenetic results were obtained from direct preparations and/or short term (1-10 days) culture. Four tumors were near tetraploid, and 16 were near diploid. Three tumors had apparently normal karyotypes Seventeen tumors demonstrated numerical changes, deletions, and/or non-reciprocal translocations. Two tumors contained double minutes. In at least two tumors, structural abnormalities were noted for chromosomes 1,5,7,9,11 or 17. The most consistent change was an i(17q), present in 5 cases. Strikingly, in 3 of these 6 tumors, the i(17q) was the only structural abnormality observed. Tumor specific loss of a sex chromosome was the only other change noted. An i(17q) is not specific for pediatric PNET-MB, since it is also seen in myeloid leukemias and other solid tumors. However, it may be a primary change related to tumor development and/or progression of PNET-MB. Clinically, there was no correlation between cytogenetics and pathology of the tumors, size of the tumor, extent of metastasis or surgical resection. All of the patients are alive to date, however longer follow-up times may reveal differences amongst these patients that correlate the cytogenetic findings with prognosis.

*22 SEARCH FOR A NEW KIND OF ANTIONCOGENE ON HUMAN CHROMOSOME 22q. - FACTS AND FANCIES. K.D.ZANG and N. BLIN, Institute of Human Genetics, University of Saarland, 665~ Homburg, W.Germany.

Loss o f chromosome 22(q) is a typical event i n the majority of meningiomas and is a non-random event in several other tumors, frequently existing as a mosaic condition. This finding led to the assumption of a hypothetical regulatory gene whose (heterozygous) loss could induce unlimited cell proliferation. - Recent molecular studies confirm the loss of genes on 22q in those tumors. In contrast to the RB locus present data do not prove, however, the homozygous loss of any sequence on 22q of the tumors in question. So both a recessive and an intermediate, an independent and an interactive antloncogene action might be possible.