Stanford School of Medicine

Surgical Pathology Criteria

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Pleomorphic Lipoma


  • Neoplasm of mature fat containing atypical cells, restricted in location to the dermis or subcutis of the posterior neck, upper back or shoulders

Diagnostic Criteria

  • Must be located in subcutis or dermis of posterior neck, upper back and shoulders
  • Variable amount of adult fat
    • 10-90% of lesion
    • Rarely fat free, see below
    • No lipoblasts
  • Atypical cells range from rare to frequent
    • Hyperchromatic enlarged nuclei
    • May form semicircle of nuclei (floret cells)
    • May be in fatty or non-fatty stromal areas
  • Bundles of dense ropey collagen
  • Stroma may be myxoid
    • Vessels may be prominent, arborizing, thick walled
    • Mast cells may be numerous
  • CD34 positive, usually extensive
  • Occasionally may display same variants as seen in spindle cell lipoma
    • Vascular pleomorphic lipoma
      • Branching dilated or cleft like-spaces
        • Papillary projections of tumor cells into the spaces
        • Spaces usually cell free
      • Spaces lined by endothelial cells with lymphatic phenotype
        • D2-40 positive, CD31 focal or negative
      • Previously termed pseudovascular
        • Based on studies without D2-40
      • Recognized based on location, areas of typical pleomorphic or spindle cell lipoma patterns and CD34 positvity
    • Fibrous pleomorphic lipoma
      • Abundant fibrous stroma
      • Bundles of collagen
      • EVG negative
      • Recognized based on location, areas of typical pleomorphic or spindle cell lipoma patterns and CD34 positvity
    • Fat free (or almost free)
      • May include above variant patterns
      • May be predominantly myxoid
      • Plexiform or curvilinear vasculature and vascular hyalinization may be prominent
      • Recognized by location, CD34 reactivity and presence of areas with typical features of pleomorphic or spindle cell lipoma
    • Rare tumors combined with hibernoma have been reported
      • No distinct clinical features
  • Frequent histologic overlap with spindle cell lipoma
    • Contains small spindle cells with scant cytoplasm

Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting : July 29, 2007
Updates: May 25, 2009; July 26, 2009

Supplemental studies


  CD34 100%, generally extensive
  bcl2 70-100%
  CD99 positive
  S100 fat cells only


Immunohistochemistry of lipomatous tumors
  MDM2 CDK4 p16
Atypical lipomatous tumor 45-100% 84-92% 78-97%
Dedifferentiated liposarcoma 55-95 90-100 90
Myxoid / round cell liposarcoma 0-4 0-4 0
Pleomorphic liposarcoma 0 0 0
Lipoma 0-4 0-2 0
Spindle cell and pleomorphic lipoma 0-25 0-6 20
Angiomyolipoma 0 0  
Hibernoma 0 0 positive, variable
Lipoblastoma 0 (1 case) 0 (1 case) positive (1 case)

Genetic analysis

  • Spindle cell lipoma and pleomorphic lipoma demonstrate the same genetic findings
    • Abnormalities of chromosome 16 resulting in deletions of 16q13-qter
    • Frequent deletions within 13q
FISH/PCR of lipomatous tumors
Atypical lipomatous tumor 90-100% 72-100% 75-100% 69-100%
Dedifferentiated liposarcoma 100% 100% 100% 100%
Myxoid liposarcoma 20%      
Spindle cell / pleomorphic lipoma Negative Negative Negative Negative
Angiolipoma Negative      
Lipoma, NOS Negative Negative Negative Negative
Sarcomas 0-40% 0% 0% 0%
  • Spindle cell / pleomorphic lipoma showed 89% chromosome 12 polysomy
  • Differential Diagnosis

    Spindle Cell Lipoma vs. Pleomorphic Lipoma

    • We consider these to be part of a spectrum
    • Mixtures are common
    • If atypical cells are present, location becomes definitional
      • Restricted to posterior neck, upper back, shoulders

    Pleomorphic Lipoma vs Atypical Lipomatous Tumor

    • The diagnosis of tumors composed of mature fat with atypia depends upon the location
      • In the dermis and subcutis of the posterior neck, upper back or shoulders, it is considered pleomorphic lipoma
      • In all other locations, it is considered atypical lipomatous tumor
    • Pleomorphic lipoma MDM2 and CDK4 negative, while most ALT are positive
    • Ropey collagen and extensive CD34 staining support pleomorphic lipoma

    Pleomorphic Lipoma Fat Necrosis
    At least scattered large eccentric nuclei Small central nuclei
    No prominent foamy cell population Foamy cells frequently fill spaces of dead adipocytes
    Ropy collagen No ropy collagen
    Restricted to back of neck, upper back and shoulders Various locations

    Pleomorphic Lipoma Pleomorphic Hyalinizing Angiectatic Tumor
    No intracytoplasmic hemosiderin Intracytoplasmic hemosiderin
    No aggregates of large vessels Aggregates of vessels with hyalinized walls and fibrin
    Ropy collagen No ropy collagen
    Restricted to back of neck, upper back and shoulders Various locations
    Both are CD34 positive


    • Rare
      • In one report, 1/10 the incidence of spindle cell lipoma
    • Most middle aged to older
    • Restricted to dermis and subcutis of posterior neck, upper back or shoulders
      • Histologically identical tumors in other sites are best considered atypical lipomatous tumors
        • Very little experience to permit prediction of behavior
    • Rarely familial or multiple
    • Recurrence is rare
      • Aggressive recurrence and dedifferentiation do not occur
      • Conservative excision is generally sufficient

    Grading / Staging / Report

    • Grading and staging are not applicable
    • Mangerial category
      • Ia (Local excision is almost always curative; metastasis never occurs)


    Lipogenic tumors

    CD34 positive neoplasms (frequent and strong)


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    • Fletcher CDM, Unni KK, Mertens F. Pathology and Genetics of Tumours of Soft Tissue and Bone, World Health Organization Classification of Tumours 2002
    • Weiss SW, Goldblum JR. Enzinger and Weiss's Soft Tissue Tumors, 4th edition, 2001
    • Dal Cin P, Sciot R, Polito P, Stas M, de Wever I, Cornelis A, Van den Berghe H. Lesions of 13q may occur independently of deletion of 16q in spindle cell/pleomorphic lipomas. Histopathology. 1997 Sep;31(3):222-5.
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    • Mandahl N, Mertens F, Willen H, Rydholm A, Brosjo O, Mitelman F. A new cytogenetic subgroup in lipomas: loss of chromosome 16 material in spindle cell and pleomorphic lipomas. J Cancer Res Clin Oncol. 1994;120(12):707-11.
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    • Enzinger FM, Harvey DA. Spindle cell lipoma. Cancer. 1975 Nov;36(5):1852-9.
    • Sachdeva MP, Goldblum JR, Rubin BP, Billings SD. Low-fat and fat-free pleomorphic lipomas: a diagnostic challenge. Am J Dermatopathol. 2009 Jul;31(5):423-6.
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