Definition
Fatty neoplasm characterized by myxoid stroma, signet ring lipoblasts, regular small round cells and/or a prominent arborizing vascular pattern
Alternate/historical terms
Round cell liposarcoma (for cellular cases)
Diagnostic Criteria
Various patterns composed of histologic features described below, may be mixed
Classical paucicellular pattern
Predominently myxoid
Scant cellularity
Arborizing vascularity
May lack lipoblasts
Pulmonary edema-like
Numerous microcysts
May lack lipoblasts
Sheets of lipoblasts Large fat cells with admixed lipoblasts
Cellular
Sheets of back to back uniform round cells
Must lack pleomorphism (see Pleomorphic Myxoid Liposarcoma below)
Must be at least 25% cellular for this designation
Pure cellular tumors may lack myxoid areas
Must have at least focal lipoblasts
Associated with significant metastatic potential
Histologic features seen in various patterns described above
Myxoid, paucicellular stroma Arborizing, plexiform capillary network
Chicken wire appearance
Thin-walled vessels
May be compressed and obscured in some non-myxoid patterns
Signet ring lipoblasts
Smaller than adult fat cells
Usually single, clear fat vacuole
Crescent or scalloped nuclei
Uniform round cells
Do not contain fat vacuoles
Small uniform nuclei with granular chromatin and prominent nucleoli
May be larger than cells in paucicellular areas
May occasionally be spindled
Microcysts
Contain granular eosinophilic material
Occasionally large and irregular
Hypocellular areas around small to medium size arteries and veins
All types lack pleomorphic cells
Exception: may be seen in rare recurrences
Features seen in rare cases
Cords of cells with myxoid or hyalinized stroma
Dedifferentiation as in usual dedifferentiated liposarcoma
Non-fatty differentiation
Cartilage or bone
Smooth or skeletal muscle
Pleomorphic myxoid liposarcoma has been reported in young patients
(Alaggio)
12 of 82 liposarcomas age 22 and under
Typical myxoid pattern merging with hypercellular foci with marked pleomorphism and increased, atypical mitotic figures
70% mortality within 36 months
Lacks CHOP translocations of usual myxoid type
Not clear if this should be considered a variant of myxoid type, pleomorphic type, a mixed type, or a separate type
Robert V Rouse MD
Original posting: August 4, 2007
Supplemental studies
Immunohistology
S100 stains mature fat cells and lipoblasts but is rarely of diagnostic use
CD34 negative or stains rare small cells
MDM2 and CDK4 generally negative
Genetic analysis
FUS/CHOP
t(12;16)(q13;p11) in 90% of cases
EWS/CHOP t(12;22)(q13;q12) in remainder
Spindle cell / pleomorphic lipoma showed 89% chromosome 12 polysomy
Differential Diagnosis
Myxoid Liposarcoma Lipoblastoma / Lipoblastomatosis
Maturation if present, occurs towards periphery
Maturation if present, occurs towards center of lobules
Rare <20, very rare <10
Very rare >20, rare >10
May have hypercellular areas
Uniformly hypocellular
Virtually always deep
May be superficial or deep
t(12;16) or t(12;22)
Abnormalities involving 8q(11-13)
Myxoid Liposarcoma Spindle Cell Lipoma with Myxoid Stroma
Infrequent prominent spindle cell component
Prominent spindle cell component
Prominent "chicken wire" vascular pattern
Lacks "chicken wire" vascular pattern
No dense collagen bundles
Dense collagen bundles
Very rare in subcutis or dermis
Usually in subcutis or dermis
CD34 negative or scattered small cells
CD34 widely positive
t(12;16) or t(12;22)
Frequent abnormalities of chromosomes 13 or 16
Myxoid Liposarcoma Atypical Lipomatous Tumor
No large atypical nuclei
Large atypical nuclei present
Prominent "chicken wire" vascular pattern
Lacks "chicken wire" vascular pattern
Rare as a primary lesion in retroperitoneum
Frequently occurs in retroperitoneum
MDM2 and CDK4 4% by immunohistology but 1/5 MDM2 by FISH
MDM2 and CDK4 most positive
Myxoid Liposarcoma Chondroid Lipoma
No chondroid matrix
Chondroid matrix
Prominent "chicken wire" vascular pattern
Lacks "chicken wire" vascular pattern
Cells more uniform
Cells frequently variable in size
Myxoid Liposarcoma Myxolipoma / Angiomyxolipoma
Prominent "chicken wire" vascular pattern
Lacks "chicken wire" vascular pattern
May have lipoblasts
Lacks lipoblasts
Very rare in subcutis or dermis
Usually in subcutis or dermis
CD34 negative or scattered small cells
CD34 widely positive in myxoid areas
t(12;16) or t(12;22)
t(7;13) or t(8;12) reported
Myxoid Liposarcoma Myxofibrosarcoma
Lipoblasts frequent
No lipoblasts
Vacuoles in lipoblasts are clear
Vacuoles, if present, contain material similar to adjacent myxoid stroma
Lacks pleomorphic cells
At least focally pleomorphic
Rare in subcutis
Frequent in subcutis
t(12;16) or t(12;22)
No consistent abnormalities
Pure Cellular Myxoid Liposarcoma Small Round Blue Cell Tumors (Various)
Lipoblasts frequent
No lipoblasts
Lacks significant pleomorphism
May be pleomorphic
No immunologic evidence of differentiation
Specific markers may be positive
t(12;16) or t(12;22)
Specific translocations may be present
Clinical
Rare <20 years, very rare <10 years of age
Myxoid liposarcoma is the most common type under age 20
Good prognosis, with similar behavior to adults
Most common in thigh
Other sites include popliteal, groin, buttock
Rare in retroperitoneum
May metastasize to this site
Apparent primary retroperitoneal tumors appear to be atypical lipomatous tumors genetically (de Vreeze)
Very rare in subcutis
Prognosis
Low cellularity tumors may metastasize, but only rarely
Cellular (25% of area) tumors frequently metasasize
Rate of metastasis is related to proportion of tumor that is cellular
Metastases frequently delayed
Median time 5-6 years
Most frequent sites are retroperitoneum, mediastinum, spine
Grading / Staging / Report
Grading is determined by cellularity and designated paucicellular and cellular
Cellular
Sheets of back to back uniform cells
Cells may be larger than in paucicellular areas
May have more granular chromatin and prominent nucleoli
Degree of cellularity must be specified
25% cellular defined as cellular myxoid liposarcoma
Associated with significant metastatic potential
French Federation of Cancer Centers System grading scheme for adult sarcomas
Tumor differentiation score = 2 if paucicellular, 3 if cellular
Mitotic index
Score 1 0-9 mitoses per 10 hpf (0.1744 sq mm)
Score 2 10-19 mitoses per 10 hpf
Score 3 >19 mitoses per 10 hpf
Tumor cell necrosis
Score 0 No necrosis on any slide (one slide per 2 cm tumor diameter)
Score 1 <50% of tumor is necrotic on slides examined
Score 2 >50% of tumor is necrotic on slides examined
Final Grade (add the three scores above)
Grade 1 Sum of scores = 2 or 3
Grade 2 Sum of scores = 4 or 5
Grade 3 Sum of scores = 6 or more
Use TNM Staging
The surgical pathology report should contain or address the following:
Location
Type of resection or biopsy
Histologic diagnosis
Managerial category III (Local recurrence common; Metastasis occurs)
Extent of tumor cell necrosis
Grade
Paucicellular vs. cellular
Stage
Size
Depth (dermis, subcutis, below fascia, body cavity)
Margins
Involved
Not involved
If under 2 cm give all such distances and sites
If over 2 cm give minimum distance and site
Results of supplementary studies if performed
Relationship to other specimens from the same patient
Lists
Lipogenic tumors
Soft tissue lesions that frequently are prominently myxoid
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
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Rubin BP, Dal Cin P. The genetics of lipomatous tumors. Semin Diagn Pathol. 2001 Nov;18(4):286-93.
Siebert JD, Williams RP, Pulitzer DR. Myxoid liposarcoma with cartilaginous differentiation. Mod Pathol. 1996 Mar;9(3):249-52.
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Shanks JH, Banerjee SS, Eyden BP. Focal rhabdomyosarcomatous differentiation in primary liposarcoma. J Clin Pathol. 1996 Sep;49(9):770-2.
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Behranwala KA, Roy P, Giblin V, A'hern R, Fisher C, Thomas JM. Intra abdominal metastases from soft tissue sarcoma. J Surg Oncol. 2004 Sep 1;87(3):116-20.
Orvieto E, Furlanetto A, Laurino L, Del Tos AP. Myxoid and round cell liposarcoma: a spectrum of myxoid adipocytic neoplasia. Semin Diagn Pathol. 2001 Nov;18(4):267-73.
Binh MB, Sastre-Garau X, Guillou L, de Pinieux G, Terrier P, Lagace R, Aurias A,
Alaggio R, Coffin CM, Weiss SW, Bridge JA, Issakov J, Oliveira AM, Folpe AL. Liposarcomas in young patients: a study of 82 cases occurring in patients younger than 22 years of age. Am J Surg Pathol. 2009 May;33(5):645-58.
de Vreeze RS, de Jong D, Tielen IH, Ruijter HJ, Nederlof PM, Haas RL, van Coevorden F. Primary retroperitoneal myxoid/round cell liposarcoma is a nonexisting disease: an immunohistochemical and molecular biological analysis. Mod Pathol. 2009 Feb;22(2):223-31.
