LAUSR

To the Editor: We read with interest the recent study by Chung et al reporting three distinctive myxoid-fibroblastic soft tissue tumors in children characterized by two unusual PLAG-1 fusions, involving YWHAZ and EEF1A genes as translocation partner in two and one case, respectively. While PLAG1-YWHAZ was previously identified in two cases, one with histological diagnosis of fibroblastic lipoblastoma, EEF1A1-PLAG1 is a novel finding. We have recently come across a case of a 2 year-old child presenting with an encapsulated sub-fascial oval mass with polylobulated margins, measuring 28 × 24 × 14 mm, located in the dorsal region, which was completely excised (Figure 1A). Based on the histological findings, a diagnosis of lipoblastoma was given. The tumor displayed a prevalent adipose component, characterized by rather uniform lobules of adipocytes (Figure 1B) and separated by thick fibrous septa. Cytologic atypia or clear evidence of lipoblasts were absent. Scattered foci of a primitive myxoid mesenchyma were present (Figure 1C,D). Immunostains showed S-100 positivity in the adipocytic component, while CD34 highlighted scattered cells within myxoid foci (Figure 1E,F) and desmin was negative. Archer FusionPlex-targeted RNA sequencing analysis performed on paraffin-embedded material detected a fusion between EEF1A1 gene at chr6:74230723 (NM_001402.5) and PLAG1 at chr8:57083748 (NM_002655.2). Similar to what previously described, in our case, the entire exon 1 of EEF1A1 merged with exon 3 of PLAG1. The fusion involved the 50 regulatory region of EEF1A1, leading to promoter swapping and increased PLAG1 transcription, with no protein contribution from EEF1A1.