Twenty-seven patients carrying marker chromosomes were previously collected, characterized by cytogenetic techniques, and identified by stepwise fluorescence in situ hybridization (FISH) with alpha-satellite DNA probes. Clinical features of 22 patients are described here and compared to other patients with marker chromosomes similarly identified and reported in the literature.

Tumors of the soft tissues are classified histogenetically according to their phenotypic resemblance to normal adult tissue, Here we describe molecular approaches that make it possible to distinguish between one class of these tumors, rhabdomyosarcoma, and other small-, round-cell tumors. W e show that the ascertainment of specific genotypic changes can be used to distinguish further between the embryonal and alveolar subtypes of rhabdomyosarcoma. W e tested our model in two ways: first, in a retrospective analysis of diagnostically problematic cases of undifferentiated, small-cell tumors and, second, in a blind study of pediatric tumors. Rhabdomyosarcoma was correctly identified in all cases using this strategy alone. The underlying simplicity of the strategy used to define rhabdomyosarcoma subtypes with molecular markers suggests a model by which tumors can be unequivocally identified, which may apply equally well to other human solid tumors.

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We report the third known case of mesenchymal hamartoma of the liver (MHL) with a balanced translocation involving a common breakpoint, 19q13.4. A common clonal chromosome abnormality appears to characterize an important subset of MHL, some of which may be low-grade neoplasms. We found no consistent karyotype abnormality in a post-treatment sample of embryonal sarcoma of the liver (ESL). Reports of coexistent MHL and ESL in two patients and detection of 19q abnormalities in two ESLs appear to support Stocker's hypothesis of a histogenetic link between these two rare liver lesions. More data are needed to clarify this relationship. It is possible that MHLs are etiologically heterogenous and may be developmental disorders, disruptions, or neoplasms.