Infantile fibrosarcoma, also known as congenital fibrosarcoma, is very rare, accounting for less than 1% of all childhood cancers. This tumor originates from connective fibrous tissue at the ends of long bones and involves surrounding soft tissue. It usually occurs in children younger than 2 years; around one-third of cases are present at birth and most are present in the first year of life. It typically presents as a painless mass that ranges in size from 1-20 cm. The distal extremities are sites of predilection, but any anatomic site may be affected. The t(12;15)(p13;q25) chromosomal translocation helps distinguish this fibrosarcoma from other fibrous lesions of childhood.

Infantile fibrosarcomas have a better prognosis than the adult form, with a 5-year survival rate of 84% seen in one study.