NR1D1‐rearranged soft tissue tumour: A clinicopathological and molecular analysis of four additional cases

Aims Nuclear receptor subfamily 1 group D member 1 ( NR1D1 )‐rearranged soft tissue tumour is a newly described entity with an epithelioid morphology and a potential for aggressive behaviour. Largely due to under‐recognition, this tumour type has not yet been widely acknowledged. Herein, we report four additional cases to further expand its clinicopathological and molecular spectrum. Methods and results Four mesenchymal tumours with NR1D1 rearrangement were identified from our consultation files. There were one male and three females with ages ranging from 19 to 47 years (median = 28.5 years). Tumour occurred in the tongue, neck, hip and index finger, respectively. Histologically, two tumours were composed predominantly of epithelioid cells; one tumour had admixed epithelioid‐spindle cells and one tumour consisted of monomorphic small round to ovoid cells. By immunohistochemistry, none of the tumours expressed lineage‐specific markers. Targeted RNA‐sequencing identified NR1D1 fusions in all four tumours, the partner genes being MAML2 , MAML3 , KMT2A and NCOA2 , respectively. The novel MAML3 and NCOA2 rearrangements were confirmed by fluorescence in‐situ hybridisation analysis. On follow‐up (2–23 months), one patient experienced local recurrence due to incomplete resection and one patient developed lung metastasis. The other two patients were alive without disease. Conclusions This study adds more support for NR1D1 ‐rearranged soft tissue tumour as an emerging entity. The occurrence of two additional tumours in the head and neck region, description of a small round cell variant and identification of novel MAML3 , KMT2A and NCOA2 partners further expand its clinicopathological and molecular spectrum. More studies on larger series are necessary to validate the fully malignant potential of NR1D1 ‐rearranged soft tissue tumour.