Challenging dedifferentiated liposarcoma identified by MDM2-amplification, a report of two cases
- Suvi Lokka†1,
- Andreas H Scheel†1, 2Email author,
- Sebastian Dango3, 4,
- Katja Schmitz2,
- Rudolf Hesterberg3,
- Josef Rüschoff1 and
- Hans-Ulrich Schildhaus2
© Lokka et al.; licensee BioMed Central Ltd. 2014
Received: 7 February 2014
Accepted: 16 July 2014
Published: 28 July 2014
Liposarcoma is the most frequent soft tissue sarcoma. Well differentiated liposarcoma may progress into dedifferentiated liposarcoma with pleomorphic histology. A minority additionally features myogenic, osteo- or chondrosarcomatous heterologous differentiation. Genomic amplification of the Mouse double minute 2 homolog (MDM2) locus is characteristic for well differentiated and dedifferentiated liposarcomas. Detection of MDM2 amplification may supplement histopathology and aid to distinguish liposarcoma from other soft tissue neoplasia.
Here we present two cases of dedifferentiated liposarcoma with challenging presentation. Case 1 features a myogenic component. As the tumour infiltrated the abdominal muscles and showed immunohistochemical expression of myogenic proteins, rhabdomyosarcoma had to be ruled out. Case 2 has an osteosarcomatous component resembling extraosseous osteosarcoma. The MDM2 status was determined in both cases and helped making the correct diagnosis. Overexpression of MDM2 and co-overexpression of Cyclin-dependent kinase 4 is demonstrated by immunohistochemistry. The underlying MDM2 amplification is shown by fluorescence in situ hybridisation. Since low grade osteosarcoma may also harbour MDM2 amplification it is emphasised that the amplification has to be present in the lipomatous parts of the tumour to distinguish liposarcoma from extraosseous osteosarcoma.
The two cases exemplify challenges in the diagnoses of dedifferentiated liposarcoma. Liposarcoma often has pleomorphic histology and additionally may feature heterologous components that mimic other soft tissue neoplasms. Amplification of MDM2 is characteristic for well differentiated and dedifferentiated liposarcomas. Determination of the MDM2 status by in situ hybridisation may assist histopathology and help to rule out differential diagnoses.
KeywordsDedifferentiated Liposarcoma Liposarcoma with osteoblastic component MDM2 Fluorescence in situ hybridisation
Benign and malignant lipomatous tumors as listed by the current WHO-definition and MDM2 -status
Spindle cell lipoma
Well differentiated liposarcoma/atypical lipomatous tumor
Intermediate, locally aggressive
Histomorphology of DDLPS usually shows remains of ALT with an abrupt shift to dedifferentiated neoplastic tissue. The dedifferentiated tissue is most commonly non lipogenic and pleomorphic, reminiscent of undifferentiated pleomorphic sarcoma (formerly called malignant fibrous histiocytoma). Additionally, heterologous differentiation occurs in about 10% of DDLPS and may present as myogenic, osteo/chondrosarcomatous or angiosarcomatous. Thus DDLPS may mimic a broad spectrum of soft tissue tumours. The clinical prognosis of DDLPS is better than for other high grade sarcoma and is not affected by the presence of heterologous differentiation.
In this report we present two cases of DDLPS with challenging presentations. Both tumours featured heterologous components imitating other soft tissue sarcoma. MDM2 amplification was detected by FISH and helped to rule out potential differential diagnosis.
Case #1, clinical presentation
Histologic and molecular findings
Case #2, clinical presentation
A 66 year old male patient presented with acute abdomen. The pain was pronounced in the lower right abdomen. Emergency surgery was performed and revealed a ruptured cystic mass of the lower right abdominal wall with connection to the abdominal cavity. En bloc resection was performed. The mass was found to be contained in the soft tissue without connection to the pelvic bones. Given the emergency situation and rupture, excision in toto could not be guaranteed.
Histologic and molecular findings
Gross examination showed a 20 × 9 × 2.5 cm specimen with yellow-whitish, smooth surface. Cross sections showed soft and fatty tissue. The wall showed areas with solid, partially mineralized tissue with lamellar macroscopic appearance.
Course of disease
The patient was transferred to a medical centre specialized in abdominal and plastic surgery. Wide excision of the tumour area was performed about one month after initial surgery. Intraoperative two tumours on the small intestine were noticed and excised. Histology confirmed tumour implants of the liposarcoma both of which had been locally excised in sano. The patient recovered from the extended surgical procedures and no signs of recurrent disease were detectable during follow-up CT- and ultrasound-scans one year later.
Two cases of neoplasm of the lower abdominal wall were resolved as dedifferentiated liposarcomas. Each tumour featured mixed morphology, one with myofibroblastic and one with osteoblastic component. Histopathology was supplemented with detailed immunohistochemistry and in situ hybridization for MDM2. Both tumours showed high MDM2 amplification which is an almost pathognomonic finding given the localization and age of the patients.
ALT and DDLPS usually show a characteristic genomic amplification of 12q13-15 including the proto-oncogenes MDM2 (12q14.3-15) and CDK4 (12q14). Amplification may be detected by comparative genome hybridization or by FISH. CDK4 is often coamplified with MDM2 and the gene products may be detected by IHC. Ubiquitin ligase MDM2 accelerates protosomal degradation of master tumour suppressor protein p53 while cell cycle associated kinase CDK4 phosphorylates and activates the retinoblastoma gene product (Rb)[7, 8]. Physiologically CDK4 is itself activated by D cyclines during G1 progression and inhibited by p16 (INK4a). Conversely p53 point mutations are rarely found in ALT and DDLPS.
The most widely used technique to determine the MDM2 status is currently dual colour FISH. Two probes specific for 12q14 and for the centromeric region of chromosome 12 are employed to detect amplification or polysomy. Cases are dichotomously classified by the ratio of MDM2 to centrosome; ≥2.0 are regarded as amplified and <2.0 as non-amplified. At least 50 non overlapping neoplastic cells should be counted. In our own hands application of the threshold is usually not required since ALT and DDLPS invariably show high amplifications with clusters of >10 copies [Figures 2D,3D].
Sensitivity of the FISH analysis has been reported to be 93.5%-100% in a case-dependent manner[6, 9]. It also has a high specificity in distinguishing lipoma from ALT. Benign lipomatous lesions do not harbour MDM2 amplifications[6, 10]. Spindle cell lipoma are reported to frequently have chromosome 12 polysomy while ALT and DDLPS close to always show MDM2 amplifications. On the other hand, myxoid liposarcomas and most pleomorphic liposarcomas do not harbour MDM2 amplifications. An exception from the rule of thumb that pleomorphic liposarcomas are MDM2 negative are cutaneous and subcutanous pleomorphic liposarcoma which may be MDM2 amplified in very rare cases. A recent study could demonstrate that peripheral undifferentiated sarcomas with MDM2 amplification correspond to DDLPS, even if a well-differentiated component was not present.
Overall, few non-liposarcomatous tumours are known to have increased MDM2 gene copy numbers. Most notably low grade osteosarcoma arising on the surface of bone may feature 12q14 amplifications while extraosseous osteosarcoma are complex genomic sarcoma without recurrent MDM2 amplifications.
The two cases exemplify challenges in the diagnosis of DDLPS. Case #1 showed little remaining well differentiated liposarcomatous tissue and featured a myogenic component. Therefore, most important differential diagnosis was rhabdomyosarcoma. Localisation, epidemiology and molecular findings render this possibility unlikely: IHC for Myogenin was negative and the MDM2 amplification is not observed in tumours of myogenic origin.
Case #2 featured a striking osteosarcomatous component which could also reflect presence of an extraosseous osteosarcoma. Given the localisation close to a fascia ossifying myositis would be benign second differential diagnoses. Transitions into atypical lipomatous tissue were noticed and under the hypotheses of DDLPS hybridisation for MDM2 was performed. Low grade Osteosarcoma (OS) may also harbour amplified MDM2. Thus, the detection of MDM2-amplification in the osteosarcomatous parts is not suited to distinguish between low grade OS and DDLPS. However, the amplification in our case was present in all parts of the tumour, including the atypical adipocytes. Thus the malignant character of the atypical adipose tissue, i.e. the liposarcomatous tissue was confirmed. Also, the tumour did not have contact to bone and extraosseous OS do not harbour MDM2 amplifications. Thus, the combination of patient age, localisation, morphology and MDM2 status strongly argues for the osteosarcomatous tissue to be heterologous component of a DDLPS.
The current standard therapy of DDLPS is wide excision. No consensus exists about the minimal length of the resection margins and the widest resection possible should be archived. This is particularly challenging in the retroperitoneum which may explain the high rates of local recurrences of DDLPS (20-100% depending on the respective study). DDLPS may spread to distant sites in 15-20% of cases while ALT do not metastasise. Case #2 exemplifies that scattered DDLPS tissue may easily spawn tumour implants. Both patients were in good health one year after treatment and showed no signs of recurrent disease. However, given the slow-growing behaviour of DDLPS careful follow-up investigations are necessary.
The recurrent MDM2 amplification might be a key to targeted therapy of DDLPS: Experimental MDM2-inhibitors have been successfully employed in vitro to reactivate p53 and mediate apoptosis. While the first generation of MDM2 inhibitors proved to be clinically intolerable several newly developed substances are currently undergoing phase I trials. Should they translate into approved drugs the MDM2 status might become a predictive biomarker.
Liposarcoma is the most frequent soft tissue neoplasm. About 40% are well differentiated liposarcoma which may progress into dedifferentiated liposarcoma. The clinical prognosis is better compared to other high grade soft tissue sarcoma.
Dedifferentiated liposarcoma has pleomorphic histomorphology. The diagnosis is facilitated by the demonstration of remaining well differentiated liposarcomatous tissue.
A minority of cases may present a heterologous differentiation of myogenic, osteo-/chondrosarcomatous or angiosarcomatous appearance. These have to be distinguished from sarcoma of other origin.
Detection of MDM2 and CDK4 amplification and coexpression by FISH and IHC has a high specificity and may support classification of challenging cases.
Written informed consent was obtained from the patients for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor of this journal.
Cyclin dependent kinase 4
Fluorescence in situ hybridization
French Fédération Nationale des Centres de Lutte Contre le Cancer grading system
Haematoxylin and eosin
Murine double-minute 2
The authors would like to thank Sara Hugo for excellent technical assistance.
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