Сongenital infantile fibrosarcoma with a non-canonical TPM3-NTRK1 fusion transcript: a case report and a literature review

Infantile fibrosarcoma (IFS) is a rare malignant soft tissue tumor characterized by local invasion, a low rate of distant metastasis (1–13%), and manifestation during the first years of life. Overall survival rates range from 89 to 94%, event-free survival rates – from 81 to 84%. Classic IFS is characterized by t(12;15)(p13;q25) translocation resulting in the formation of the ETV6-NTRK3 fusion transcript. However, over the past few years, there have been numerous reports of IFS-like tumors with non-canonical genetic aberrations (BRAF, NTRK1, MET genes) whose prognosis is less predictable. Here we report a rare case of congenital IFS with involvement of subcutaneous fat, indolent course and a non-canonical TPM3-NTRK1 fusion transcript identified in the soft tissue and intradermal tumor components with different histological features. The patient’s parents gave their consent to the use of their child’s data, including photographs, for research purposes and in publications. The literature review explores modern algorithms for the diagnosis and treatment of IFS in children, including the use of new therapies, such as tropomyosin receptor kinase inhibitors, as well as algorithms for detecting NTRK1, NTRK2, NTRK3 gene rearrangements in solid neoplasms in general, and soft tissue tumors in particular.