PRRX1::NCOA1 Rearranged Fibroblastic Tumour: A New Report With a Brief Literature Review of an Uncommon Neoplasm

The increased application of next-generation sequencing technologies in challenging spindle cell neoplasms has given rise to the discovery of a novel PRRX1::NCOA1 rearranged fibroblastic neoplasm, which is not yet included in the World Health Organization (WHO) classification of soft tissue tumours. We report on an additional example of a well-circumscribed, monomorphic, oval- to spindle-shaped cellular tumour, which had patchy reactivity for smooth muscle actin and S100 on immunohistochemistry and a PRRX1::NCOA1 fusion transcript. To date, 43 tumours have been described in the literature. We review the clinicopathologic and molecular features of reported tumours and discuss relevant differential diagnoses. Available data suggest indolent behaviour; however, a long-term follow-up is required to ascertain the risk of recurrence or malignant behaviour.