Fusion genes aiding the diagnosis of soft tissue tumours of the oral cavity: From bench to bedside.

Soft tissue tumours (STT) are a heterogeneous group of benign, malignant, and intermediate/borderline mesenchymal tumours. In the oral and maxillofacial region, less than 3% of all lesions correspond to benign STT and <1% are sarcomas. Overlapping microscopic features may lead to quite challenging diagnostic processes. Translocations and fusion genes are frequent, and type-specific genetic alterations are detected in these tumours. The detection of such alterations by classic cytogenetic, FISH, RT-PCR or NGS can help to define the diagnosis. This narrative review aims to review fusion genes reported for STT that affect the oral cavity and their use in diagnostic molecular pathology. Basic concepts regarding mechanisms of fusion genes formation are presented to clarify this information for surgical pathologists. The chromosomal rearrangements and fusion genes of adipocytic, fibroblastic and myofibroblastic, vascular, pericytic, smooth muscle, skeletal muscle, chondro-osseous, and uncertain origin STT are summarised. The advance in molecular pathology techniques has led not only to a better understanding of the molecular pathogenesis of STT, but also to the development of helpful diagnostic tools. Therefore, it is important for the oral and head and neck pathologists to familiarise with the signature rearrangements and fusion genes for each tumour.