Pathology: phosphaturic mesenchymal tumour

Phosphaturic mesenchymal tumour

Osteomalacia. Serology for FGF23 was 1300 (normal < 180)

  • Cellular; spindle-stellate cells with patternless distribution

  • Pale eosinophilic cytoplasm with occasional clear vacuoles

  • Ovoid nuclei with angulation, hyperchromasia and minimal atypia; inconspicuous mitotic activity

  • Basophilic matrix with cystic degeneration

  • RNA-seq: negative

Phosphaturic mesenchymal tumour

  • Hypocellular; spindle-stellate cells with patternless distribution

  • Pale eosinophilic cytoplasm

  • Ovoid nuclei with minimal atypia; inconspicuous mitotic activity

  • Basophilic matrix with areas of "grungy" calcification; occasional small vessels with thick hyalinized walls

  • RNA-seq: FN1::FGFR1 gene fusion

Phosphaturic mesenchymal tumour

  • Hypocellular; sheets of polygonal cells, some of which are in lacunae-like spaces

  • Pale amphophilic cytoplasm

  • Ovoid nuclei with mild atypia; inconspicuous mitotic activity

  • Basophilic matrix with areas of "grungy" calcification; scattered osteoclast-type giant cells; cystic degeneration

  • IHC: ERG, SATB2

  • RNA-seq: FN1::FGFR1 gene fusion

Phosphaturic mesenchymal tumour

  • Cellular; spindle-epithelioid cells with patternless distribution

  • Pale amphophilic cytoplasm with indistinct cell borders

  • Monomorphic ovoid nuclei; inconspicuous mitotic activity

  • Cystic degeneration with pools of proteinaceous fluid; prominent branching capillary vasculature

  • IHC: D2-40, ERG, SATB2

  • RNA-seq: negative