Bone & Soft Tissue Pathology

Dedifferentiated Liposarcoma with Divergent Rhabdomyosarcomatous Differentiation

Jean-Michel Coindre
Institut Bergonie
Bordeaux, France


Case History:
A 62-year-old man presented with a 15 cm tumor developed in the retroperitoneum with involvement of the small intestine

This tumor had been resected in 1992 with a portion of the small intestine.


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Figure 1 - The tumor seemed to be well demarcated but with adhesion to the deep part of the small intestine.
Figure 2 - The adjacent tissue was composed of mature adipocytes arranged in lobules separated by thick fibrous septa.
Figure 3 - The tumor was composed of spindle and pleomorphic eosinophilic cells arranged in fascicles.

Figure 4 - The tumor cells tended to have an abundant eosinophilic cytoplasm with racket-like contours.
Figure 5 - These tumor cells showed a wide range of cell shapes from globular to tadpole-like, with atypical nuclei and mitoses.
Figure 6 - These tumor cells showed a wide range of cell shapes from globular to tadpole-like, with atypical nuclei and mitoses.

Figure 7 - A few atypical, hyperchromatic cells were visible in the fibrous septa separating adjacent adipocytic tissue.
Figure 8 - A few atypical, hyperchromatic cells were visible in the fibrous septa separating adjacent adipocytic tissue.
Figure 9 - The tumor cells were diffusely and strongly positive for desmin. At that time, the diagnosis was pleomorphic rhabdomyosarcoma.


Clinical Follow-up and Complementary Techniques
A local recurrence occurred 6 years later with multiple nodules involving the retroperitoneum, small and large bowels, the bladder and abdominal wall. The tumor was partly resected but the patient died 5 months later.

The resected tumor was similar to the primary and showed areas of poorly differentiated spindle cell sarcoma, pleomorphic rhabdomyosarcoma and large areas of sclerosing liposarcoma.

Immunohistochemistry showed positivity of tumor cells for desmin, myogenin, MDM2 and CDK4 on both primary and recurrent tumors. MDM2 and CDK4 were also positive on some atypical cells seen in the sclerosing liposarcomatous component.

FISH and Q-PCR showed a large amplification of MDM2 and CDK4.

CGH-array showed a rather simple DNA profile with amplifications of 12q13-14 including MDM2, CDK4 and MYF genes and 1p32 including JUN gene.

Diagnosis
Dedifferentiated liposarcoma with divergent rhabdomyosarcomatous differentiation.

Discussion
Dedifferentiated liposarcoma is a term first introduced by Evans in 1979 [1] to describe liposarcomas containing a mixture of well differentiated and poorly differentiated areas either within the same primary tumor or in the recurrence or metastasis. It is considered as a malignant adipocytic tumor showing progression from atypical lipomatous tumor/well differentiated liposarcoma to non-lipogenic sarcoma of variable grade. About 90% of dedifferentiated liposarcomas arise de novo while 10% occur in recurrences. The risk of dedifferentiation is higher in deep seated tumors, particularly in the retroperitoneum, and is probably a time-dependent phenomenon [2]. Numerous reports have supported the concept of dedifferentiated liposarcomas with two series of 32 and 155 cases [3, 4]. It represented 18% of liposarcomas in a recent large series [5].

Tumors occurred in late adult life with no sex predilection, most commonly in the retroperitoneum (2/3 of cases), extremities, spermatic cord and trunk. Occurrence in head and neck and in subcutaneous tissue is rare. In our experience, 60% of retroperitoneal sarcomas are liposarcomas, half of which are dedifferentiated liposarcomas.

Dedifferentiated liposarcoma usually presents as a large painless mass, with a median size of 20 cm in the retroperitoneum. Radiological imaging may suggest the diagnosis by showing the coexistence of a fatty component with a non-fatty solid one. Prognosis of dedifferentiated liposarcoma is mainly dominated by local recurrences (40 to 60%), particularly in the retroperitoneum, with a quite low metastatic potential (15 to 20%). The most important prognostic factor is location with a poor prognosis for retroperitoneal tumors. Neither histological grade nor extent of dedifferentiation is of prognostic value [3, 4].

The gross appearance of dedifferentiated liposarcoma is often helpful for the diagnosis. It usually consists of multinodular yellow (fatty) masses containing firm tan-gray areas corresponding to dedifferentiated foci. Necrosis is often observed.

Histologically, dedifferentiated liposarcoma is defined by the association of atypical lipomatous tumor/well-differentiated liposarcoma areas and a non-lipogenic sarcoma, usually with an abrupt transition between the two components. Dedifferentiated areas exhibit a wide morphological spectrum. Most cases show areas of high grade sarcoma resembling pleomorphic MFH, myxofibrosarcoma, fibrosarcoma or malignant hemangiopericytoma. Low grade dedifferentiation resembling low grade myxofibrosarcoma, well-differentiated fibrosarcoma or fibromatosis is the only dedifferentiated component in about 10% of cases [4]. A "meningothelial-like" whorling pattern of dedifferentiation often associated with ossification has been described [6, 7]. In about 5 to 10% cases, the dedifferentiated component is a divergent differentiation with myogenic or osteo-chondrosarcomatous elements. An angiosarcomatous component has also been reported. Myosarcomatous differentiation is the most frequent [8, 9] but must be established with both morphological features and immunohistochemical profile, and specific muscle markers such as h-caldesmon and myogenic should be used. We recently reviewed a series of sarcomas with a myogenic differentiation developed in the internal trunk for which initial diagnoses were leiomyosarcoma, pleomorphic rhabdomyosarcoma, malignant mesenchymoma and dedifferentiated liposarcoma with divergent myosarcomatous differentiation, and showed that most pleomorphic rhabdomyosarcomas and malignant mesenchymomas were actually dedifferentiated liposarcomas with a myogenic differentiation. Moreover, dedifferentiated liposarcomas with a myogenic component had a low metastatic potential, similar to conventional dedifferentiated liposarcomas and significantly lower than the metastatic potential of leiomyosarcomas [10].

Contrary to this histological complexity, the genomic profile of dedifferentiated liposarcoma is relatively simple and uniform. Cytogenetics shows ring and giant chromosomes with a normal karyotype in other respects [11, 12]. As shown by CGH techniques, these ring and giant markers are composed of amplified sequences of the 12q13-14 chromosome region. This amplicon is mainly composed of MDM2 and CDK4 genes [13]. This basic profile is similar to that observed in atypical lipomatous tumor/well differentiated liposarcoma. MDM2 inhibits P53 and therefore decreases apoptosis and tends to increase cell survival. CDK4 phosphorylates Rb gene product, which no longer interacts with E2F transcription factors, and the cell cycle proceeds through the G1-S checkpoint. In summary, the biological consequence of the 12q13-14 amplicon is both to decrease apoptosis and to increase cell proliferation. In addition to this amplicon, dedifferentiated liposarcomas also usually show coamplification of chromosomes 1 or 6. The two most frequent coamplifications are located on 1p32 and 6q23 chromosome regions. These amplifications are exclusive and never seen together in the same tumor. Characterization by CGH-array of the minimal region of amplification shows that the target genes are JUN in the 1p32 band and ASK1 in the 6q23 band. ASK1 is a MAP3 kinase involved in the JNK signaling pathway [14]. Amplification and overexpression of ASK1 activates JNK, which phosphorylates different target proteins, leading to the activation of some proteins including JUN and inactivation of other proteins, in particular PPAR gamma. It has been demonstrated that PPAR gamma plays a key role in adipocytic differentiation, and therefore, amplification of ASK1 gene inhibits adipocytic differentiation. JUN is an oncogene which also inhibits PPAR gamma via C/EBP beta. Therefore, dedifferentiation in liposarcoma may be explained by amplification and overexpression of ASK1 or JUN genes. In summary, amplification of MDM2 and CDK4, which are seen in both atypical lipomatous tumor/well differentiated liposarcoma and dedifferentiated liposarcoma, may be responsible for the malignant tumor process, whereas amplification of other genes such as ASK1 and JUN may explain inhibition of adipocytic differentiation in dedifferentiated liposarcomas.

Re-evaluation of retroperitoneal sarcomas in adults as well as these molecular data make it possible to formulate criteria for the diagnosis of dedifferentiated liposarcomas: 1- any poorly differentiated sarcomas including so-called pleomorphic MFH, fibrosarcomas, malignant hemangiopericytomas, myxofibrosarcomas [15] and inflammatory MFH [16] as well as pleomorphic rhabdomyosarcomas and malignant mesenchymomas [10] developed in the retroperitoneal or in paratesticular areas are most likely dedifferentiated liposarcomas; 2- the best criterion for the diagnosis is the presence of an atypical lipomatous tumor/well differentiated liposarcoma area, so the clue is to sample and carefully examine the surrounding adipocytic tissues; 3- in some cases, this well differentiated component is missing and molecular abnormalities may be useful. CGH-array, which shows a simple DNA profile with MDM2 and CDK4 amplifications in association with one or a few coamplifications, is the most specific technique, and could be the gold standard in the next years; 4- at present, immunohistochemistry is a useful tool for daily practice, provided one uses the proper antibodies: IF2 clone for MDM2 and DCS-31 for CDK4 [17]. For problematic cases, Q-PCR [18] and especially FISH are reproducible and can be used on formalin fixed paraffin-embedded tissues. In our experience, MDM2 amplification is constant in dedifferentiated liposarcomas and CDK4 amplification is present in 90% of cases. These amplifications are not seen in benign lipomatous tumors and are rare in other sarcomas.

References
  1. Evans HL. Liposarcoma. A study of 55 cases with a reassessment of its classification. Am J Surg Pathol 1979; 3: 507-23.

  2. Fletcher CDM, Unni KK, Mertens F (Eds): World Health Organization Classification of Tumours. Pathology and Genetics of Tumours of Soft Tissue and Bone. IARC Press: Lyon 2002.

  3. McCormick D, Mentzel T, Beham A, Fletcher CDM. Dedifferentiated liposarcoma. Clinicopathologic analysis of 32 cases suggesting a better prognostic subgroup among pleomorphic sarcomas. Am J Surg Pathol 1994; 18:1213-23.

  4. Henricks WH, Chu YC, Goldblum JR, Weiss SW. Dedifferentiated liposarcoma. A clinicopathologic analysis of 155 cases with a proposal for an expanded definition of dedifferentiation. Am J Surg Pahol 1997; 21: 271-81.

  5. Dalal KM, Kattan MW, Antonescu CR, Brennan MF, Singer S. Subtype specific prognostic nomogram for patients with primary liposarcoma of the retroperitoneum, extremity, or trunk. Ann Surg 2006; 244: 381-91.

  6. Fanburg-Smith JC, Miettinen M. Liposarcoma with meningothelial-like whorls: a study of 17 cases of a distinctive histological pattern associated with dedifferentiated liposarcoma. Histopathology 1998; 33: 414-24.

  7. Nascimento AG, Kurtin PJ, Guillou L, Fletcher CD. Dedifferentiated liposarcoma: a report of nine cases with a peculiar neurolike whorling pattern associated with metaplastic bone formation. Am J Surg Pathol 1998; 22: 945-55.

  8. Tallini G, Erlandson RA, Brennan MF, Woodruff JM. Divergent myosarcomatous differentiation in retroperitoneal liposarcoma. Am J Surg Pathol 1993; 17: 546-56.

  9. Evans HL, Khurana KK, Kemp BL, Ayala AG. Heterologous elements in the dedifferentiated component of dedifferentiated liposarcoma. Am J Surg Pathol 1994; 18: 1150-7.

  10. Coindre JM, Guillou L, Hostein I et al. Myosarcomatous differentiation in dedifferentiated liposarcomas does not increase the risk of metastatic dissemination. Comparative study between conventional dedifferentiated liposarcomas, dedifferentiated liposarcomas with divergent myosarcomatous differentiation and pure leiomyosarcomas of retroperitoneal and paratesticular regions. Mod Pathol 2005; 18 (Suppl1): 12A.

  11. Mertens F, Fletcher CD, Dal Cin P, et al. Cytogenetic analysis of 46 pleomorphic soft tissue sarcomas and correlation with morphologic and clinical features: a report of the CHAMP Study Group. Genes Chromosomes Cancer 1998; 22: 16-25.

  12. Pedeutour F, Forus A, Coindre JM, et al. Structure of the supernumerary ring and giant rod chromosomes in adipose tissue tumors. Genes Chromosomes Cancer 1999; 24: 30-41.

  13. Chibon F, Mariani O, Derre J, et al. A subgroup of malignant fibrous histiocytomas is associated with genetic changes similar to those of well-differentiated liposarcomas. Cancer Genet Cytogenet 2002; 139: 24-9.

  14. Chibon F, Mariani O, Derre J et al. ASK1 (MAP3K5) as a potentiel therapeutic target in malignant fibrous histiocytomas with 12q14-q15 and 6q23 amplifications. Genes Chromosomes Cancer 2004; 40: 32-7.

  15. Coindre JM, Mariani O, Chibon F, et al. Most malignant fibrous histiocytomas developed in the retroperitoneum are dedifferentiated liposarcomas: a review of 25 cases initially diagnosed as malignant fibrous histiocytoma. Mod Pathol 2003 ; 16: 256-62.

  16. Coindre JM, Hostein I, Maire G, et al. Inflammatory malignant fibrous histiocytomas and dedifferentiated liposarcomas: histological review, genomic profile, and MDM2 and CDK4 status favour a single entity. J Pathol 2004; 203: 822-30.

  17. Bui Nguyen Binh M, Sastre X, Guillou L, et al. MDM2 and CDK4 immunostainings are useful adjuncts in diagnosing well-differentiated and dedifferentiated liposarcoma subtypes. A comparative analysis of 561 soft tissue neoplasms with genetic data. Am J Surg Pathol 2005; 29: 1340-7.

  18. Hostein I, Pelmus M, Aurias A, Pédeutour F, Mathoulin-Pélissier S, Coindre JM. Evaluation of MDM2 and CDK4 amplification by real-time PCR on paraffin wax-embedded material: a potential tool for the diagnosis of atypical lipomatous tumours/well-differentiated liposarcomas. J Pathol 2004; 202: 95-102.