Intra-abdominal desmoplastic small round-cell tumor. Report of 19 cases of a distinctive type of high-grade polyphenotypic malignancy affecting young individuals.

Nineteen cases of a distinctive type of malignant small-cell tumor are presented. The main features of the entity are as follows: a predilection for adolescent males (mean age: 18.6 years); predominant or exclusive intra-abdominal location, with only inconstant and secondary organ involvement; nesting pattern of growth; focal rhabdoid features; intense desmoplastic reaction; immunohistochemical reactivity for epithelial [keratin, epithelial membrane antigen (EMA)], neural [neuron-specific enolase (NSE)], and muscle (desmin) markers; and highly aggressive behavior. It is proposed that this represents yet another member of the continuously enlarging and evolving family of small round (blue) cell tumors of infancy and childhood that features, more than any other member of this group, the capacity for simultaneous multidirectional phenotypical expression.