Poorly differentiated, neuron-specific enolase positive round cell tumor with two translocations t(11;22) and t(21;22).

The authors describe a highly malignant, disseminated round cell tumor originating in the ninth rib of a 14-year-old boy. Extensive studies by means of light and electron microscopic examination, histocytochemistry and immunocytochemistry and cytogenetic analysis revealed an undifferentiated, neuron-specific enolase positive round cell tumor with a unique karyotype: 45,XY,-21,t(11;22)(q23;q11), der(22)t(21;22)(q11.2;p11). Thus, despite the absence of definite morphologic features, such as Homer-Wright rosettes, neurosecretory granules and cytoplasmatic processes, these findings suggest a neuroectodermal origin of this bone tumor.