Atypical Lipomatous Tumor and Liposarcoma



Atypical Lipomatous Tumor and Liposarcoma


Elizabeth A. Montgomery, MD





Key Facts


Terminology



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


Clinical Issues



  • Accounts for 40-45% of all liposarcomas


  • Occurs most frequently in deep soft tissues of limbs followed by retroperitoneum, abdominal cavity, paratesticular region, and mediastinum


  • Usually presents as deep-seated, painless, and slowly enlarging tumor mass


  • Lesions located in surgically amenable soft tissues recur only rarely after complete excision


  • Neoplasms arising in intraabdominal, retroperitoneum, mediastinum, or spermatic cord often recur repeatedly and may cause death


  • Variable risk of dedifferentiation in extremities (< 2%) and retroperitoneum (> 25%)


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


  • Middle-aged to elderly adults


  • Intermediate (locally aggressive but nonmetastasizing) malignant mesenchymal tumor


Microscopic Pathology



  • Atypical adipocytes, atypical stromal cells, lipoblasts



    • Adipocytes show striking variations in size and shape


    • Enlarged hyperchromatic nuclei


  • Lipoma-like subtype


  • Sclerosing subtype


  • Inflammatory subtype


  • Spindle cell subtype







A large lipomatous tumor on the shoulder of a male patient is shown. This image was taken at the time of an operation to remove the lesion.






Histologic examination of ALT shows striking variations in size and shape of lipogenic cells, as well as scattered enlarged cells with enlarged hyperchromatic nuclei.


TERMINOLOGY


Abbreviations



  • Atypical lipomatous tumor (ALT)


Synonyms



  • Well-differentiated liposarcoma (WDLS)


Definitions



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


CLINICAL ISSUES


Epidemiology



  • 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


Presentation



  • Deep-seated, painless, slowly enlarging tumor mass


Treatment



  • Complete surgical excision


Prognosis



  • In surgically amenable sites



    • 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%)


IMAGE FINDINGS


General Features



  • Best diagnostic clue



    • Circumscribed, lobular mass


  • Location



    • Deep soft tissues


  • Size



    • Variable


    • Usually > 5 cm


  • Morphology



    • Circumscribed, lipomatous lesion


MACROSCOPIC FEATURES


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


Size



  • May attain very large size


MICROSCOPIC PATHOLOGY


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


Grade



  • Intermediate (locally aggressive but nonmetastasizing) malignant mesenchymal tumor


ANCILLARY TESTS


Cytogenetics



  • Supernumerary ring and giant marker chromosomes



    • Contain amplified sequences originating from 12q14-15 region


    • MDM2, CDK4, SAS, HMGIC are amplified


In Situ Hybridization



  • MDM2 and CDK4 amplification can be identified by FISH-technique

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Jul 8, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Atypical Lipomatous Tumor and Liposarcoma

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