Congenital fibrosarcoma with a novel complex 3-way translocation t(12;15;19) and unusual histologic features.

Congenital mesenchymal tumors are diagnostically challenging as they are rare and may feature overlapping patterns between several benign, low-grade, and tumors of intermediate malignancy, including myofibromatosis, myofibroma/hemangiopericytoma, congenital fibrosarcoma, and inflammatory myofibroblastic tumor. Their immunophenotype is either silent or minimally expressive, and their ultrastructural features are generically consistent with "fibroblastic/myofibroblastic" differentiation. Cytogenetic analysis allows refined diagnoses, improved classifications, and bettering of our therapeutic armamentarium. However, genotype/phenotype correlations continue rendering novel findings that must be examined for their potential value in diagnosis and treatment. We describe a retroperitoneal congenital fibrosarcoma with an unusually bland histopathology and novel 3-way t(12;15;19) translocation involving chromosome bands 12p13.2, 15q25.3, and 19p13.1, associated with trisomies 8, 11, and 20. Fluorescence in situ hybridization showed one fusion signal in the normal chromosome 12p13.2 and break-apart 3'ETV6 and 5'ETV6 signals in the rearranged 12p13.2 and 15q25.3, respectively. The importance of molecular diagnosis and genotype-phenotype correlations is emphasized.