Soft tissue

• Locally aggressive mesenchymal tumor composed of mature adipocytes and stromal cells with at least focal cytologic atypia
• Adipocytic component and background cellular constituents vary in concentration and lead to several recognizable morphologic subtypes

• Use of the terminology atypical lipomatous tumor (ALT) and well differentiated liposarcoma (WDL) is based on a tumor's location in the body and primarily relates to resectability
  • Tumors are morphologically and genetically identical, with the variation in terminology intended to avoid both undertreatment and overtreatment
• Tumors located in the periphery have no risk of metastasis
  • For such lesions, complete resection is generally curative
  • For these tumors, the designation as sarcoma is inappropriate and the term ALT is preferred
• If the tumor is deep seated (retroperitoneum, mediastinum, spermatic cord), the chance of achieving negative margins is significantly diminished and the risk of local recurrence, dedifferentiation (DDL) and death are increased
  • Lesions are best regarded as true sarcomas and the terminology of well differentiated liposarcoma is more appropriate
• Suggestion: use of atypical lipoma is not recommended

• Most common adipocytic malignancy (40 - 45% of all liposarcomas)
• Peak age in adults is between 40 - 60 years
• Very rare in children but can be associated with Li-Fraumeni syndrome (Hum Pathol 2018;71:41, Pediatr Dev Pathol 2010;13:218)

• Most common site is the deep thigh of the lower extremity, followed by retroperitoneum, trunk, head and neck region and spermatic cord
• Numerous anatomic sites have been reported, including the subcutis and skin

• 36 year old woman with gluteal mass (World J Surg Oncol 2006;4:33)
• 43 year old woman with abdominal fullness and weight gain (Hinyokika Kiyo 2010;56:697)
• 73 year old man with mesenteric tumor (Case Rep Oncol 2011;4:178)
• Multiple cases of oral and salivary gland liposarcomas (Mod Pathol 2002;15:1020)

Images hosted on other servers:

Images hosted on other servers:

Contributed by Michael Clay, M.D. and AFIP



Morphologic variability:




Metaplastic change:

• HMB45

• Ring or giant marker / rod chromosomes derived from 12q13-15 in almost all cases
• Amplifications of the 12q12-21 (Virchows Arch 2012;461:67)
• MDM2 and CDK4, by FISH or real time PCR, can differentiate from other sarcomas (Hum Pathol 2006;37:1123, Am J Surg Pathol 2007;31:1476)
  • See Am J Surg Pathol 2015;39:1433 for recommendations on when to utilize FISH in well differentiated tumors
• Carboxypeptidase M amplification has also been reported (Mod Pathol 2009;22:1541)
• Other rearrangements include amplifications of 10p11-14 and complex rearrangements involving chromosomes 8 and 12 (Virchows Arch 2012;461:67, Oncol Rep 2005;13:649)

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A retroperitoneal tumor is surgically resected and the microscopic image provided is representative of the entire lesion. Ancillary FISH testing is positive for MDM2 amplification. What is the diagnosis?

1. Lipoma
2. Myxofibrosarcoma
3. Myxoid liposarcoma
4. Pleomorphic lipoma
5. Well differentiated liposarcoma

E. Well differentiated liposarcoma. Given the findings of a retroperitoneal mass composed of a proliferation of variably sized adipocytes intermixed with rare atypical cells characterized by enlarged, hyperchromatic nuclei, the best diagnosis is well differentiated liposarcoma. Evidence of MDM2 amplification by FISH testing supports the diagnosis. A is incorrect, since although deep seated and large lipomas can occur, these lesions lack atypical nuclei and do not have 12q13-15 amplification. B is incorrect because myxofibrosarcomas are extremely rare in the retroperitoneum and although low grade lesions have scattered cells with enlarged, hyperchromatic nuclei, they do not have 12q13-15 amplification. C is incorrect because myxoid liposarcoma tumor cells lack significant atypia, are typically evenly distributed in a prominent myxoid stroma with delicate branching vasculature and do not have 12q13-15 amplification. D is incorrect because pleomorphic lipomas are most frequently seen in the head and neck region and do not have 12q13-15 amplification.

Comment Here

Reference: Atypical lipomatous tumor / well differentiated liposarcoma

Which of the following is true about atypical lipomatous tumor / well differentiated liposarcomas (ALT / WDL)?

1. Frequently present in the upper trunk / back of the neck in adults
2. Have genomic alterations at 8q11-13
3. Lack the ability to metastasize
4. Must contain lipoblasts
5. Show a predilection to metastasize to other soft tissue sites

C. Lack the ability to metastasize. ALT / WDL cannot metastasize unless it progresses to a dedifferentiated liposarcoma. A is incorrect because spindle cell lipomas show this predilection. B is incorrect because lipoblastomas have PLAG1 gene fusions, which is located at 8q11-13. D is incorrect since ALT / WDL neither need nor always have lipoblasts. E is incorrect because myxoid liposarcoma shows the unusual predilection among fatty tumors to metastasize to other soft tissue sites.

Comment Here

Reference: Atypical lipomatous tumor / well differentiated liposarcoma