Pleomorphic Lipoma

Definition

• 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
  • If located in other sites, we consider it to be atypical lipomatous tumor
• 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

Immunohistology

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

Differential Diagnosis

• Spindle cell lipoma
• Atypical lipomatous tumor
• Fat necrosis
• Pleomorphic hyalinizing angiectatic tumor

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

Clinical

• 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)

Lists

Lipogenic tumors

• Angiomyolipoma
• Hemosiderotic Fibrohistiocytic Lipomatous Lesion
• Hibernoma
• Lipofibromatosis
• Lipoma
• Lipomatosis
• Lipoblastoma / lipoblastomatosis
• Pleomorphic lipoma
• Spindle cell lipoma
• Atypical lipomatous tumor
• Liposarcoma
  • Dedifferentiated
  • Myxoid
  • Pleomorphic
  • Unclassified
• Atypical Spindle Cell Lipomatous Tumor

CD34 positive neoplasms (frequent and strong)

• Angiosarcoma
• Cellular angiofibroma
• Dermatofibrosarcoma protuberans
• Epithelioid sarcoma
• Glomus tumor
• Gastrointestinal stroma tumor
• Giant cell angiofibroma
• Hemangioendothelioma
• Hemangiopericytoma
• Inflammatory fibroid polyp
• Ischemic fasciitis
• Juxtagomerular cell tumor
• Kaposi sarcoma
• Leukemia, myeloid
• Leukemia, acute lymphoblastic
• Liposarcoma, dedifferentiated
• Lymphangioendothelioma
• Meningioma
• Neurofibroma
• Pleomorphic hyalinizing angiectatic tumor
• Pleomorphic lipoma
• Proximal type epithelioid sarcoma
• Solitary fibrous tumor
• Spindle cell lipoma
• Superficial acral fibromyxoma
• Superficial angiomyxoma
• Superficial myofibroblastoma
• Carcinoma and melanoma are essentially never CD34 positive

Bibliography

• Kempson RL, Fletcher CDM, Evans HL, Henrickson MR, Sibley RS. Tumors of the Soft Tissues, Atlas of Tumor Pathology, AFIP Third Series, Fascicle 30, 2001
• 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.
• Rubin BP, Dal Cin P. The genetics of lipomatous tumors. Semin Diagn Pathol. 2001 Nov;18(4):286-93.
• Fletcher CD, Akerman M, Dal Cin P, de Wever I, Mandahl N, Mertens F, Mitelman F, Rosai J, Rydholm A, Sciot R, Tallini G, van den Berghe H, van de Ven W, Vanni R, Willen H. Correlation between clinicopathological features and karyotype in lipomatous tumors. A report of 178 cases from the Chromosomes and Morphology (CHAMP) Collaborative Study Group. Am J Pathol. 1996 Feb;148(2):623-30.
• 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.
• French CA, Mentzel T, Kutzner H, Fletcher CD. Intradermal spindle cell/pleomorphic lipoma: a distinct subset. Am J Dermatopathol. 2000 Dec;22(6):496-502.
• Suster S, Fisher C. Immunoreactivity for the human hematopoietic progenitor cell antigen (CD34) in lipomatous tumors. Am J Surg Pathol. 1997 Feb;21(2):195-200.
• Templeton SF, Solomon AR Jr. Spindle cell lipoma is strongly CD34 positive. An immunohistochemical study. J Cutan Pathol. 1996 Dec;23(6):546-50.
• Zelger BW, Zelger BG, Plorer A, Steiner H, Fritsch PO. Dermal spindle cell lipoma: plexiform and nodular variants. Histopathology. 1995 Dec;27(6):533-40.
• Fanburg-Smith JC, Devaney KO, Miettinen M, Weiss SW. Multiple spindle cell lipomas: a report of 7 familial and 11 nonfamilial cases. Am J Surg Pathol. 1998 Jan;22(1):40-8.
• 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.
• Zamecnik M, Michal M. Angiomatous spindle cell lipoma: Report of three cases with immunohistochemical and ultrastructural study and reappraisal of former 'pseudoangiomatous' variant. Pathol Int. 2007 Jan;57(1):26-31
• Diaz-Cascajo C, Borghi S, Weyers W. Pleomorphic lipoma with pseudopapillary structures: a pleomorphic counterpart of pseudoangiomatous spindle cell lipoma. Histopathology. 2000 May;36(5):475-6