Emerging fusion-associated mesenchymal tumours: a tabular guide and appraisal of five 'novel' entities.

Aims: The field of molecular pathology has undergone significant advancements in the clinical impact of sarcoma diagnosis, resulting in challenges to nosology of bone and soft tissue tumours. The surge in molecular data has led to the identification of novel fusions and description of new 'entities'. To illustrate this, we have selected five emerging entities with novel fusions: clear cell stromal tumour of the lung with YAP1::TFE3 fusion, GAB1::ABL1 fusion spindle cell neoplasm, NUTM1-rearranged sarcomas, NR1D1-rearranged sarcomas and calcified chondroid mesenchymal neoplasms.

Methods: Literature for the relevant case reports and case series of these five entities were reviewed and clinicopathological data was collected. Additionally, this review includes a table format of recently described fusion-associated mesenchymal neoplasms.

Results: The morphological and immunohistochemical features, along with diagnostic challenges, are discussed for each entity.

Conclusions: Here, we have provided a review of selected emerging mesenchymal neoplasms, which of these neoplasms will meet the threshold to be 'new entities' remains to be determined.