Atypical Lipomatous Tumor/Well-Differentiated Liposarcoma

Atypical Lipomatous Tumor/Well-Differentiated Liposarcoma

Thomas Mentzel, MD

Gross pathology photograph shows a well-circumscribed neoplasm of deep soft tissues with indurated, yellow-white cut surfaces.

Hematoxylin & eosin shows striking variations in size and shape of lipogenic cells, as well as scattered enlarged cells with enlarged hyperchromatic nuclei.



  • Atypical lipomatous tumor (ALT)


  • Well-differentiated liposarcoma (WDLS)


  • Intermediate (locally aggressive, nonmetastasizing) lipogenic neoplasm composed of atypical adipocytes



  • Incidence

    • Accounts for 40-45% of all liposarcomas

    • Most frequently in deep soft tissues

      • Retroperitoneum, abdominal cavity, paratesticular region, mediastinum

      • Limbs

    • May also arise in subcutaneous tissue and very rarely in skin

  • Age

    • Middle-aged to elderly adults

    • Extremely rare in childhood

  • Gender

    • M = F


  • Deep-seated, painless, and slowly enlarging tumor mass


  • Complete surgical excision


  • In surgically amenable site

    • Recur only rarely after complete excision

  • Intraabdominal, retroperitoneal, mediastinal, or paratesticular lesions

    • Often recur locally and may be fatal

  • Variable risk of dedifferentiation in extremities (< 2%) and in retroperitoneum (> 20%)


General Features

  • Best diagnostic clue

    • Circumscribed lobular mass

  • Location

    • Deep soft tissues

  • Size

    • Variable

    • Usually > 5 cm

  • Morphology

    • Circumscribed lipomatous lesion


General Features

  • Well-circumscribed lobular neoplasms

  • Color varies from yellow to white

  • Fat necrosis may be seen in large lesions

Sections to Be Submitted

  • Sample margins and representative sections of tumor

  • Look for indurated, firm areas


  • May attain very large size


Histologic Features

  • Lipoma-like subtype

    • Adipocytes show significant variation in size and shape

    • Enlarged hyperchromatic nuclei

    • Hyperchromatic and multinucleated stromal cells

    • Lipoblasts may be seen but are not essential for diagnosis

    • Involvement of large vessel walls by atypical tumor cells

    • Prominent myxoid stromal changes may be present

    • Rare chondroid stromal changes

  • Sclerosing subtype

    • Scattered bizarre stromal cells with hyperchromatic nuclei

    • Rare atypical lipogenic cells and multivacuolated lipoblasts

    • Fibrillary, collagenous stroma

  • Inflammatory subtype

    • Prominent inflammatory infiltrate (lymphocytes, plasma cells)

    • Scattered atypical lipogenic cells/lipoblasts

    • Often edematous stroma

  • Spindle cell subtype

    • Atypical lipogenic cells

    • Slightly atypical neuroid spindle cells

    • Fibrous, fibromyxoid stroma

  • Heterologous differentiation rarely seen

    • Smooth or striated muscle

    • Cartilage, bone

Predominant Pattern/Injury Type

  • Circumscribed

Predominant Cell/Compartment Type

  • Adipose

    • Atypical adipocytes, atypical stromal cells, lipoblasts


  • Intermediate (locally aggressive but nonmetastasizing) malignant mesenchymal tumor

Jul 9, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Atypical Lipomatous Tumor/Well-Differentiated Liposarcoma

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