Pathology: well-differentiated liposarcoma / Atypical lipomatous tumour

Liposarcoma, inflammatory

  • Heterogeneous lesion composed of adipocytes, inflammatory cells and atypical stromal cells

  • Adipocytes: sheets and nests of polygonal cells; abundant clear cytoplasm with mild variability in size and shape; eccentric small monomorphic nuclei

  • Inflammatory cells: admixture of lymphocytes, plasma cells, and histiocytes

  • Stromal cells: spindle-polygonal cells; eosinophilic cytoplasm; ovoid-round nuclei with prominent nucleoli, occasional multinucleation, moderate pleomorphism and inconspicuous mitotic activity

  • IHC: CDK4, MDM2

  • FISH: MDM2 amplified

The subtypes of well-differentiated liposarcoma often show morphologic overlap

Liposarcoma, lipoma-like

  • Sheets of polygonal cells

  • Abundant clear cytoplasm with mild variability in size and shape; rare multivacuolation

  • Peripherally located small monomorphic nuclei

  • FISH: MDM2 amplified

Liposarcoma, lipoma-like

  • Sheets of polygonal cells

  • Abundant clear cytoplasm with mild variability in size and shape; rare multivacuolation

  • Peripherally located small monomorphic nuclei

  • FISH: MDM2 amplified

Liposarcoma, lipoma-like

  • Infiltrative sheets of polygonal cells

  • Abundant clear cytoplasm with mild variability in size and shape; rare multivacuolation

  • Peripherally located small monomorphic nuclei

  • Background skeletal muscle has atrophy and reactive changes

  • FISH: MDM2 amplified

Liposarcoma, sclerosing

  • Sheets of polygonal cells and loose fascicles of spindle cells

  • Polygonal cells have abundant clear cytoplasm with mild variability in size and shape and rare multivacuolation; peripherally located small monomorphic nuclei

  • Spindle cells have pale eosinophilic cytoplasm; hyperchromatic ovoid nuclei with mild pleomorphism; delicate collagenous stroma

  • Polygonal cells with abundant eosinophilic cytoplasm and round, often binucleated, nuclei can often be found interspersed and/or lurking in the walls of vessels

  • FISH: MDM2 amplified

There is considerable overlap with so-called "low-grade" dedifferentiation (the latter is differentiated on low-power examination as lacking a significant interspersed lipogenic component)