Soft tissue
Adipose tissue
Atypical lipomatous tumor / well differentiated liposarcoma

Author: Vijay Shankar, M.D. (see Authors page)

Revised: 8 August 2016, last major update August 2012

Copyright: (c) 2002-2016, PathologyOutlines.com, Inc.

PubMed Search: Atypical lipomatous tumor / well differentiated liposarcoma

Definition / General
  • Low grade malignancy of relatively mature adipocytes that exhibit focal atypia
Terminology
  • Called atypical lipomatous tumor in periphery
  • Use of “atypical lipoma” is not recommended
  • Suggestion: call “well differentiated liposarcoma” in retroperitoneum or central body site and “atypical lipomatous tumor” elsewhere
Epidemiology
  • Common liposarcoma subtype (40 - 45% of liposarcomas)
  • Adults, peaks at ages 40 - 60 years
  • Very rare in children
Sites
  • Usually lower limbs, retroperitoneum, trunk, head and neck region, also paratesticular, mediastinum or subcutaneous tissue
  • Unusual sites include parotid gland, esophagus, mesentry, breast
Case Reports
Prognosis and Treatment
  • Excision; negative margins are particularly important for sclerosing subtype (Ann Surg Oncol 2004;11:78)
  • Does not metastasize unless it dedifferentiates, which is associated with shorter survival (Am J Surg Pathol 2007;31:1)
  • Subcutaneous or intramuscular tumors may recur but typically do not dedifferentiate or metastasize
  • Retroperitoneal or central body site tumors are difficult to resect with a clear margin; frequently recur, dedifferentiate and cause death
  • Sample carefully to look for dedifferentiated component
  • Retroperitoneal / intra-abdominal location is associated with the worse outcome (J Surg Res 2012;175:12)
Clinical Images

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Pelvic tumor during surgery

Gross Description
  • Circumscribed or infiltrative
  • Bulging, large (particularly in retroperitoneum), yellow-white
  • Resembles lipoma
  • Coarsely lobulated with pale, firm areas
  • Fat necrosis in large lesions
Gross Images

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Mesenteric tumor

Pelvic tumor

Tumor of mesocolon

Micro Description
  • Mature fat plus variably sized adipocytes and fibromyxoid stroma containing spindle cells with large, deep-staining nuclei and marked nuclear enlargement or pleomorphism
  • Cellularity is low and mitotic figures are uncommon
  • Usually fibrous tissue septa are present that may contain spindle cells or highly pleomorphic cells
  • Some nuclei have sharply outlined vacuoles (Lochkern)
  • Rarely heterologous differentiation
  • No/few lipoblasts
  • Rarely have no / minimal adipocytes except in recurrences
  • Some authors do not require any atypia for diagnosis of retroperitoneal tumors
  • May be associated with metaplastic bone formation (Hinyokika Kiyo 2010;56:697)
  • Rarely has low grade osteosarcomatous component (Am J Surg Pathol 2010;34:1361)

  • Tumors are subtyped, but this has no clinical significance (Semin Diagn Pathol 2001;18:258)
    • Inflammatory subtype: rare; lymphoid nodules in cellular stroma with atypical multinucleated cells; may obscure lipocytes (see inflammatory liposarcoma)
    • Lipoleiomyosarcoma subtype: liposarcoma with leiomyosarcomatous differentiation (see lipoleiomyosarcoma)
    • Lipoma-like subtype: most common subtype; scattered atypical cells; rare to frequent lipoblasts
    • Sclerosing subtype: retroperitoneal or paratesticular lesions; collagenous fibrous tissue with scattered adipocytes and atypical multinucleated stromal cells; few lipoblasts
    • Spindle cell subtype: CD34+ spindle cells in short fascicles, whorls or storiform pattern mixed with well differentiated liposarcoma component with hyperchromatic nuclei but only mild atypia
    • Mixed subtype: very common
Micro Images

Images hosted on PathOut servers:

Enlarged, dense irregular nuclei

Bizarre shaped cells

Lipoblasts are multivacuolated with atypical nuclei



Atypical cells within fibrous tissue

Lochkern cells with sharply outlined nuclear vacuoles

Floret cells



Thick collagen fibers

Thin collagen fibers

Moderately cellular (but not dedifferentiated)

Atypical cells within blood vessel walls

Metaplastic bone

Metaplastic smooth muscle



Images hosted on other servers:

Figure 2: Well circumscribed tumor

Immunostains



Various images

Cytology Description
  • Large cells with multilobulated nuclei and mature appearing adipocytes
  • May have bizarre tumor cells (Acta Cytol 2000;44:459)
Positive Stains
Negative Stains
Electron Microscopy Description
  • Pseudoinclusions due to invaginations of nuclear membrane
Molecular / Cytogenetics Description
Molecular / Cytogenetics Images

Images hosted on other servers:

(A) ring chromosome
(B) giant marker chromosome
(C) anaphase bridge



Images hosted on Nature servers:

(A) ring chromosome
(B) giant marker chromosome
(C) anaphase bridge

Differential Diagnosis
Additional References