Superficial CD34-positive fibroblastic tumour with MED12 :: chr4 intergenic :: PRDM10 fusion: A case report

Superficial CD34-positive fibroblastic tumour (SCPFT) is a rare soft tissue neoplasm of borderline malignancy. It typically presents as a painless, slow-growing, well-circumscribed subcutaneous mass in adults, most commonly in the lower limbs. It is commonly associated with PRDM10 rearrangements. A 57-year-old lady presented with a left posterior calf lump of 10 years duration. MRI showed a subcutaneous mass measuring 3.9x2.9 cm. Excision showed a moderately cellular tumour composed of spindle cells with eosinophilic cytoplasm arranged in fascicles and a vague storiform pattern. There was multi-focal moderate nuclear atypia, but no necrosis or significant mitotic activity. In some areas, the tumour cells showed lipidized cytoplasm, and focally, a haemosiderotic appearance. It stained diffusely positive for CD34 and WT1, and showed rare positive staining for SMA, S100, MUC4 and EMA. It was negative for desmin, caldesmon, ALK, SOX10, ERG, MNF116 and pan-TRK. Ki67 proliferative index was 3 % to 5 %. Archer FusionPlex Pan-Solid Tumour V2 Next-Generation Sequencing Assay detected a MED12 (exon 43) :: chr4 intergenic :: PRDM10 (exon 14) gene fusion. The surgical margins were positive for tumour, hence a repeat MRI was performed which showed changes indeterminate for post-surgical changes or small residual focus. There was no recurrence at 1 year follow-up. PRDM10 rearrangements have been reported in SCPFT. Fusion partners include MED12 . To our understanding, this is the first case of SCPFT harboring a three-way fusion that includes the intergenic region of chromosome 4 – its impact remains uncertain.