Unusual presentation of congenital infantile fibrosarcoma in seven infants with molecular-genetic analysis.

Congenital infantile fibrosarcoma (CIFS) is a rare mesenchymal tumor that primarily presents in the soft tissue of the distal extremities and occasionally in unusual locations such as the lung and retroperitoneum. Herein, we report seven cases of unusual presentations of CIFS. These cases include three in the lungs, one in the retroperitoneum with cord compression, one in the posterior trunk, one in the heart, and one infratemporal involving the sphenoid bone. All tumors demonstrated CIFS's characteristic t(12;15)(p13;q25) and associated ETV6-NTRK3 gene fusion. One of the three lung cases was previously reported as primary bronchopulmonary fibrosarcoma (PBPF), but molecular analysis of the paraffin embedded tissue revealed the ETV6-NTRK3 gene fusion consistent with CIFS. We show that CIFS may occur in unusual sites including visceral locations, and we propose that neoplasms displaying the ETV6-NTRK3 gene fusion represent the visceral components of CIFS.