Scientific and technical advances have direct impact on the day to day practice of surgical pathology. Pathologists must learn to use new findings to improve diagnostic classification and add clinically useful information in a fiscally responsible manner. The undifferentiated tumors of young people (historically referred to as small round cell tumors of infancy) are a useful example of how new information has become an important part of routine practice. This article describes a practical approach to the differential diagnosis of small round cell tumors using immunophenotypic and genetic analysis as an aid to increase confidence and diagnostic accuracy.
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