MDM2 Amplified Sarcomas: a Literature Review

diagnostics

Review MDM2 Ampliﬁed Sarcomas: A Literature Review

Raf Sciot

Department of Pathology, University Hospital, University of Leuven, 3000 Leuven, Belgium; [email protected]

Abstract: Murine Double Minute Clone 2, located at 12q15, is an oncogene that codes for an oncoprotein of which the association with p53 was discovered 30 years ago. The most important function of MDM2 is to control p53 activity; it is in fact the best documented negative regulator of p53. Mutations of the tumor suppressor gene p53 represent the most frequent genetic change in human cancers. By overexpressing MDM2, cancer cells have another means to block p53. The sarcomas in which MDM2 ampliﬁcation is a hallmark are well-differentiated liposarcoma/atypical lipomatous tumor, dedifferentiated liposarcoma, intimal sarcoma, and low-grade osteosarcoma. The purpose of this review is to summarize the typical clinical, histopathological, immunohistochemical, and genetic features of these tumors.

Keywords: MDM2 ampliﬁcation; well-differentiated liposarcoma/atypical lipomatous tumor; dedifferentiated liposarcoma; intimal sarcoma low grade osteosarcoma

1. Introduction Murine Double Minute Clone 2 is an oncogene, the function of which was first described in DNA associated with paired acentric chromatin bodies, termed double minutes, harbored in spontaneously transformed mouse 3T3 fibroblasts [1]. MDM2 (located at 12q15) codes for Citation: Sciot, R. MDM2 Amplified an oncoprotein of which the association with p53 was discovered 30 years ago. The protein Sarcomas: A Literature Review. functions as an E3 ubiquitin ligase that targets the p53 protein for proteasomal degradation. Diagnostics 2021, 11, 496. https:// Thus, the most important function of MDM2 is to control p53 activity; it is in fact the best doi.org/10.3390/diagnostics11030496 documented negative regulator of p53. For normal cells, it is of utmost importance that p53 is maintained at low levels since p53 has potent growth suppressive activities. In fact, p53 Academic Editor: David Creytens is lethal in the absence of MDM2. Mouse MDM2−/− embryos are inviable and deletion of p53 rescues these embryos. There are different mechanisms by which MDM2 can block Received: 22 February 2021 p53 activity. On the one hand, MDM2 stimulates the degradation of p53 by escorting p53 Accepted: 9 March 2021 from the nucleus to the cytoplasm and by catalyzing the ubiquitination of p53 and hence, Published: 11 March 2021 proteosomal degradation. On the other hand, MDM2 blocks the activity of intact p53 by inhibiting the p53 transactivation domain. Indeed, it is well known that p53 trans-activates Publisher’s Note: MDPI stays neutral a number of genes that mediate cell cycle arrest or apoptosis [1]. The oncogenic activities with regard to jurisdictional claims in published maps and institutional affil- of MDM2 extend beyond the regulation of p53. Thus, MDM2-mediated ubiquitination of iations. various transcription factors (ATF, E2F and others), of the retinoblastoma protein, and the histones H2A and H2B can influence cell proliferation, DNA repair, transcription, ribosome biosynthesis and cell fate. In addition, chromatin-bound MDM2 plays a key role in serine metabolism [2]. Mutations of the tumor suppressor gene p53 represent the most frequent genetic change Copyright: © 2021 by the author. in human cancers. By overexpressing MDM2, cancer cells have another means to block p53. Licensee MDPI, Basel, Switzerland. It is no surprise that tumors that show MDM2 amplification do not require p53 mutations. This article is an open access article distributed under the terms and The overall MDM2 gene amplification frequency in human cancer varies between conditions of the Creative Commons 3.5 and 4.4% [3,4]. Some gliomas, carcinomas and hematological malignancies have been Attribution (CC BY) license (https:// described to amplify MDM2, but this feature is most frequently seen in sarcomas, the topic creativecommons.org/licenses/by/ of the review. 4.0/).

Diagnostics 2021, 11, 496. https://doi.org/10.3390/diagnostics11030496 https://www.mdpi.com/journal/diagnostics Diagnostics 2021, 11, 496 2 of 15

The sarcomas in which MDM2 amplification is a hallmark are well-differentiated liposarcoma/atypical lipomatous tumor, dedifferentiated liposarcoma, intimal sarcoma, and low-grade osteosarcoma. Myxofibrosarcomas, malignant peripheral nerve sheath tumors and undifferentiated sarcomas can occasionally show MDM2 amplification as well. Very recently it was described that a rare subtype of endometrial sarcoma, characterized by BCOR rearrangement, also seems to carry MDM2 amplifications [5]. MDM2 has become a hot topic in cancer treatment, because anti-MDM2 therapy has become a reality: we actually know of molecules that block the MDM2-p53 interaction, and thus, reestablish wild type p53 activity [6–9]. First-generation small molecule inhibitors of MDM2, nutlins, were identified in 2004. Nutlin-3A, a pharmacological inhibitor of the MDM2–p53 interaction, stabilizes p53; however, its clinical efficacy is very low and severe thrombocytopenia represents a dose-limiting toxicity. Recent novel second-generation molecules that interfere with MDM2, or the MDM2–p53 interaction, seem to be more promising [2,10–12]. Interestingly, MDM2 is also used as a target in many non-neoplastic diseases, which underscores its role beyond oncology [13].

2. Well-Differentiated Liposarcoma/Atypical Lipomatous Tumor (WDL/ATL) This tumor represents the most common malignant adipocytic neoplasm and is mainly seen in middle-aged adults. The deep soft tissues of the extremities are most frequently involved (75%), followed by the retroperitoneum (20%). The groin, paratesticulum and mediastinum are also known locations. The overall mortality is zero for lesions of the extremities and more than 80% for exactly the same tumors in the retroperitoneum. There- fore, the term “atypical lipomatous tumor” is used for lesions in surgically amenable sites where excision can be curative, like the extremities, and “well differentiated liposarcoma” for tumors presenting in the retroperitoneum, spermatic cord and mediastinum, where complete removal is often not possible leading to high morbidity and mortality. Three morphological subtypes are classically described: lipoma-like, sclerosing and inflammatory [14]. In the lipoma-like variant, the basic morphological hallmark is the presence of variation in adipocyte diameter, hyperchromatic/atypical nuclei and lipoblasts (Figure1). In the sclerosing variant, scattered bizarre hyperchromatic cells and lipoblasts are seen in an extensive fibrillary stroma, varying from dens to myxoid (Figure2). This subtype is most often seen in the retroperitoneum or paratesticular area. In the inflammatory variant, mainly seen in the retroperitoneum, a lymphoplasmocytic inflammatory infiltrate predominates and obscures the adipocytic component, to the extent that it can mimic inflammatory myofibroblastic tumor, Castleman’s disease or even a lymphoma (Figure3). These phenotypic variants can be admixed in the same tumor. Whatever it looks like, WDL/ATL is characterized by giant marker and/or supernumerary ring chromosomes, both of which contain multiple copies of MDM2. This amplification results in nuclear MDM2 protein overexpression. There is frequently co-amplification of other genes of the 12q14-15 region, like CDK4, GLI1 and HMGA2, but MDM2 amplification is the main driver (Figure4). Immunohistochemistry and/or FISH for MDM2 is frequently used to support the diagnosis of WDL/ATL, FISH being much more sensitive and specific than protein detection (Figure5) [ 15,16]. MDM2 RNA ISH seems to be as performant as DNA FISH [17]. An important pitfall is the presence of nuclear MDM2 immunoreactivity in histiocytes/lipophages which are very often seen in traumatized fatty tumors. In addition, any cytoplasmic positivity is not diagnostic. The pathologist is often faced with lesions in which the histological changes are not convincing enough for WDL/ATL and thus, the differential diagnosis with an ordinary lipoma cannot be made on morphological grounds alone. This does not mean that every lipoma should be FISHed for MDM2, the following features justify the use of this test: (1) recurrent lesion, (2) deep extremity lesion larger than 10 cm in a patient over 50 years of age, (3) lesion with equivocal atypia, (4) lesion in the retroperitoneum/pelvis/abdomen, and (5) lesions not fitting the above criteria but having worrisome clinical or radiological features [18]. Diagnostics 2021, 11, x 3 of 16

larger than 10 cm in a patient over 50 years of age, (3) lesion with equivocal atypia, (4) lesion in the retroperitoneum/pelvis/abdomen, and (5) lesions not fitting the above criteria but having worrisome clinical or radiological features [18]. A lack of MDM2 amplification does not entirely preclude the diagnosis of ALT/WDL. In Li–Fraumeni syndrome, the occurrence of p53+/MDM2− ALT/WDL can be an early expression of the disease [19]. It is of interest that in the past, a well-differentiated spindle cell liposarcoma subtype was described. This group of tumors is now called atypical spindle cell lipoma, since it has a different genetic background, relating it to spindle cell lipoma, with deletion of the Rb-1 gene [20,21]. Very recently, rare cases of “dysplastic lipoma”, “anisometric cell lipoma”, or “minimally ALT” have been reported. These tumors, which do not fit neatly into the category of lipoma or ALT, show prominent variation in adipocyte size, frequent single-cell adipocytic necrosis, limited nuclear enlargement and hyperchromasia, and minimally thickened fibrous septa. These tumors do not show MDM2 amplification as determined by FISH, but are positive for MDM2 RNA-ISH. In addition, they can show deletion of the RB- Diagnostics 2021, 11, 496 1 gene on 13q14 [22–24]. Clinically, local recurrence in dysplastic lipoma is estimated3 of 15to be approximately 10%, which is intermediate between lipoma and ALT. Further studies are warranted to clarify the exact classification of these lesions.

DiagnosticsFigureFigure 2021 1.1. ,Lipoma-likeLip 11, omax -like variant of of well well-differentiated-differentiated liposarcoma liposarcoma/atypical/atypical lipomatous lipomatous tumor, tumor, showing showing the the variation variation in ad- in 4 of 16

adipocyteipocyte size, size, hyperchromatic hyperchromatic nuclei nuclei and and lipoblasts lipoblasts (a (),a ),detail detail of of lipoblasts lipoblasts with with the the typical typical punched punched-out-out nucleus nucleus in in (b (b).).

FigureFigure 2. 2.Sclerosing Sclerosing variant variant of of well-differentiated well-differentiated liposarcoma/atypical liposarcoma/atypical lipomatous lipomatous tumor, tumor, highlight- high- inglighting the scattered the scattered lipoblasts lipoblasts in a sclerotic in a sclerotic background. background.

Figure 3. Inflammatory variant of well-differentiated liposarcoma/atypical lipomatous tumor, dominated by a prominent lymphoplasmocytic infiltration. Note the atypical fat cells as well.

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Diagnostics 2021, 11, 496 4 of 15 Figure 2. Sclerosing variant of well-differentiated liposarcoma/atypical lipomatous tumor, high- lighting the scattered lipoblasts in a sclerotic background.

Diagnostics 2021, 11,Figure x 3. Inflammatory variant of well-differentiated liposarcoma/atypical lipomatous tumor, 5 of 16 Figure 3. Inﬂammatory variant of well-differentiated liposarcoma/atypical lipomatous tumor, domi- nateddominated by a prominent by a prominent lymphoplasmocytic lymphoplasmocytic inﬁltration. infiltration. Note theNote atypical the atypical fat cells fat as cells well. as well.

Figure 4. Ring chromosomeFigure 4. Ring in well chromosome-differentiated in well-differentiated liposarcoma/atypical liposarcoma/atypical lipomatous tumor. lipomatous The ring tumor.contains multiple copies of the MDM2The andring CDK4 contains gene. multiple copies of the MDM2 and CDK4 gene.

Figure 5. MDM2 expression in the lipoma-like (a), sclerosing (b), and inflammatory variant (c) of well-differentiated liposarcoma/atypical lipomatous tumor.

3. Dedifferentiated Liposarcoma Dedifferentiated liposarcoma (DDL) is defined as the transition of WDL/ATL to- wards nonlipogenic sarcoma, either in the primary tumor or in a recurrence. The well- differentiated component can be absent. A total of 90% of DDL present de novo, +/− 10% of WDL/ATL dedifferentiate into DDL. Patients are most often older than 45 years. The retroperitoneum is the most frequent site (80%), and DDL is the most frequent retroperitoneal sarcoma (Figure 6). Other sites are the deep soft tissue of the extremities, the funiculus spermaticus/paratesticulum and mediastinum. The transition to the nonlipogenic sarcoma is usually abrupt and the latter most often looks like undifferentiated pleomorphic or spindle cell sarcoma, but myxoid sarcoma-like pictures, or low grade desmoid-like areas, can be seen as well (Figures 7 and 8). Heterologous differentiation is present in up to 10%, myogenic (leiomyo-, or rhabdomyosarcoma) being most frequent, followed by osteo- or chondrosarcoma-like phenotypes [25,26]. A peculiar type is the DDL

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Diagnostics 2021, 11, 496 5 of 15 Figure 4. Ring chromosome in well-differentiated liposarcoma/atypical lipomatous tumor. The ring contains multiple copies of the MDM2 and CDK4 gene.

FigureFigure 5.5. MDM2 expression expression in in the the li lipoma-likepoma-like (a (),a ),sclerosing sclerosing (b), (b and), and inflammatory inﬂammatory variant variant (c) of (c )well of well-differentiated-differentiated lipo- liposarcoma/atypicalsarcoma/atypical lipomatous lipomatous tumor. tumor.

3. DedifferentiatedA lack of MDM2 Lamplificationiposarcoma does not entirely preclude the diagnosis of ALT/WDL. MDM2− In Li–FraumeniDedifferentiated syndrome, liposarcoma the occurrence (DDL) of is p53+/ defined as the transitionALT/WDL of can WDL/ATL be an early to- expression of the disease [19]. wards nonlipogenic sarcoma, either in the primary tumor or in a recurrence. The well- It is of interest that in the past, a well-differentiated spindle cell liposarcoma subtype differentiated component can be absent. A total of 90% of DDL present de novo, +/− 10% was described. This group of tumors is now called atypical spindle cell lipoma, since it has of WDL/ATL dedifferentiate into DDL. Patients are most often older than 45 years. The a different genetic background, relating it to spindle cell lipoma, with deletion of the Rb-1 retroperitoneum is the most frequent site (80%), and DDL is the most frequent retroperi- gene [20,21]. toneal sarcoma (Figure 6). Other sites are the deep soft tissue of the extremities, the funic- Very recently, rare cases of “dysplastic lipoma”, “anisometric cell lipoma”, or “mini- ulus spermaticus/paratesticulum and mediastinum. The transition to the nonlipogenic mally ALT” have been reported. These tumors, which do not fit neatly into the category of sarcoma is usually abrupt and the latter most often looks like undifferentiated pleo- lipoma or ALT, show prominent variation in adipocyte size, frequent single-cell adipocytic morphic or spindle cell sarcoma, but myxoid sarcoma-like pictures, or low grade des- necrosis, limited nuclear enlargement and hyperchromasia, and minimally thickened fi- moid-like areas, can be seen as well (Figures 7 and 8). Heterologous differentiation is pre- brous septa. These tumors do not show MDM2 amplification as determined by FISH, butsent are in up positive to 10%, for myogenicMDM2 RNA-ISH. (leiomyo-,In or addition,rhabdomyosarcoma) they can show being deletion most frequent, of the RB-1 fol- genelowed on by 13q14 osteo [22- or–24 chondrosarcoma]. Clinically, local-like recurrence phenotypes in dysplastic [25,26]. A lipoma peculiar is estimatedtype is the toDDL be approximately 10%, which is intermediate between lipoma and ALT. Further studies are warranted to clarify the exact classification of these lesions.

3. Dedifferentiated Liposarcoma Dedifferentiated liposarcoma (DDL) is defined as the transition of WDL/ATL to- wards nonlipogenic sarcoma, either in the primary tumor or in a recurrence. The well- differentiated component can be absent. A total of 90% of DDL present de novo, +/− 10% of WDL/ATL dedifferentiate into DDL. Patients are most often older than 45 years. The retroperitoneum is the most frequent site (80%), and DDL is the most frequent retroperitoneal sarcoma (Figure6). Other sites are the deep soft tissue of the extremities, the funiculus spermaticus/paratesticulum and mediastinum. The transition to the nonlipogenic sarcoma is usually abrupt and the latter most often looks like undifferentiated pleomorphic or spindle cell sarcoma, but myxoid sarcoma-like pictures, or low grade desmoid-like areas, can be seen as well (Figures7 and8). Heterologous differentiation is present in up to 10%, myogenic (leiomyo-, or rhabdomyosarcoma) being most frequent, followed by osteo- or chondrosarcoma-like phenotypes [25,26]. A peculiar type is the DDL with meningothelial-like whorls and metaplastic bone formation, typically seen in the retroperitoneum (Figure9)[ 27]. In the past, an inflammatory type of malignant fibrous histiocytoma, rich in neutrophils and also occurring in the retroperitoneum, was described. This tumor represents another phenotype of DDL [26]. In fact, DDL can mimic any type of sarcoma and MDM2 immunohistochemistry/FISH should be part of the panel of tests in Diagnostics 2021, 11, x 6 of 16

with meningothelial-like whorls and metaplastic bone formation, typically seen in the retroperitoneum (Figure 9) [27]. In the past, an inflammatory type of malignant fibrous histiocytoma, rich in neutrophils and also occurring in the retroperitoneum, was described. Diagnostics 2021, 11, 496 This tumor represents another phenotype of DDL [26]. In fact, DDL can mimic any6 oftype 15 of sarcoma and MDM2 immunohistochemistry/FISH should be part of the panel of tests in any sarcoma occurring at any site, certainly if it is undifferentiated and pleomorphic. anyThus, sarcoma if one occurringis confronted at any with site, an certainly undifferentiated if it is undifferentiated pleomorphic andor spindle pleomorphic. cell sarcoma, Thus, ifeven one if is there confronted is virtually with anno undifferentiatedfat, the finding of pleomorphic MDM2 expression/amplification or spindle cell sarcoma, will even indi- ifcate there that is it virtually concerns no a fat,DDL the [28 finding]. An interesting of MDM2 b expression/amplificationut unusual form of dedifferentiation will indicate is thatthe so it- concernscalled homologous a DDL [28 ].lipogenic An interesting dedifferentiation, but unusual which form is ofcharacterized dedifferentiation by big is atyp- the so-calledical lipoblasts, homologous exactly lipogenicas seen in dedifferentiation,pleomorphic liposarcoma which is [29 characterized]. MDM2 expression by big atypical usually lipoblasts,is very prominent exactly asin seenthe dedifferentia in pleomorphicted area liposarcoma as opposed [29 ].to MDM2the well expression-differentiated usually part is(Figure very prominent 7). Once dedifferentiation in the dedifferentiated is present, area the as opposed tumor gains to the metastatic well-differentiated potential but part is (Figureless aggressive7). Once dedifferentiationthan other pleomorphic is present, sarcomas. the tumor Recurrence gains metastatic is seen potential in at least but is40% less of aggressivecases, metastatic than other rates pleomorphic vary between sarcomas. 15 and 30% Recurrence and tumor is- seenrelated in atdeath least is 40% +/− 28% of cases, at 5- metastaticyear follow rates-up. varyThis figure between is without 15 and 30%any doubt and tumor-related much higher deathat 10 to is 20 +/ years− 28% [25 at]. 5-yearRecent follow-up.studies indicate This figurethat high is without grade dedifferentiation any doubt much and higher the presence at 10 to 20of yearsmyogenic [25]. (particu- Recent studieslarly rhabdomy indicateoblastic) that high dedifferentiation grade dedifferentiation correlate and with the a presenceworse prognosis of myogenic [30–32 (partic-]. As in ularlyWDL/ATL, rhabdomyoblastic) complete surgical dedifferentiation resection is the correlate mainstay with of a worsetreatment. prognosis DDL also [30– 32harbors]. As inhigh WDL/ATL, level amplifications complete surgical of 12q14 resection-15, including is the mainstay the MDM2 of treatment.and CDK4 DDLgenes. also The harbors degree highof MDM2 level amplificationsamplification ofmight 12q14-15, affect includingclinical outcome, the MDM2 althoughand CDK4 prospectivegenes. The studies degree are ofneeded MDM2 to amplificationobjectivate this might finding affect [32 clinical]. As opposed outcome, to althoughWDL/ATL, prospective DDL shows studies otherare ge- needednetic changes, to objectivate as 6q23 this and finding 1p32 [co32-].amplifications. As opposed to In WDL/ATL, this respect, DDL JUN shows (1p32.2) other is of genetic inter- changes,est since asits 6q23 amplification and 1p32 co-amplifications.is probably involved In thisin the respect, progressionJUN (1p32.2) from WDL/ATL is of interest to sinceDDL. itsAnother amplification feature isthat probably favors involveddedifferentiation in the progression might be the from loss WDL/ATL of HMGA2 to overexpression, DDL. Another featurewhich is that frequent favors in dedifferentiation DDL [33]. A recent might study be theon the loss integrated of HMGA2 exomeoverexpression, and RNA sequenc- which ising frequent of 115 DDLs in DDL showed [33]. A elegantly recent study that gains on the of integrated several somatic exome copy and- RNAnumber sequencing alternations of 115and DDLs chromosomal showed elegantlyrearrangements, that gains including of several the somatic DNM3OS copy-number-fusion genes alternations and the loss and of chromosomalG0S2 and DGAT2 rearrangements,, contribute to including the cell cycle the DNM3OSprogression-fusion and impairment genes and the of adipogenesis loss of G0S2 and[34]DGAT2. , contribute to the cell cycle progression and impairment of adipogenesis [34].

FigureFigure 6. 6.MRI MRI picturespictures of of a a big big retroperitoneal retroperitoneal tumor tumor in in an an 82-years-old 82-years-old male male patient. patient.

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Figure 7. Abrupt transition of the well-differentiated lipoma-like liposarcoma part to the non-lipo- Figure 7. Abrupt transition of the well-differentiated lipoma-like liposarcoma part to the non-lipogenic genic sarcomatous part (a). Detail of both parts (b,c), and MDM2 expression in both parts (d,e). sarcomatous part (a). Detail of both parts (b,c), and MDM2 expression in both parts (d,e).

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Figure 8. Scar-like phenotype of a dedifferentiated liposarcoma, H&E (a), and MDM2 stain (b). FigureFigure 8. 8. Scar Scar-like-like phenotype phenotype of of a a dedifferentiated dedifferentiated liposarcoma, liposarcoma, H&E H&E ( a(a),), and and MDM2 MDM2 stain stain ( b(b).).

Figure 9. Meningothelial-like whorls and metaplastic bone formation in a retroperitoneal dediffer- FigureFigure 9. 9. Meningothelial-like whorls and metaplastic bone formation in a retroperitoneal dedifferentiated liposarcomaMeningothelial-like (H&E). whorls and metaplastic bone formation in a retroperitoneal dedifferen- tiatedentiated liposarcoma liposarcoma (H&E). (H&E).

4.4. Intimal Intimal S Sarcoma Sarcomaarcoma IntimalIntimal sarcomas sarcomas are are very very rare rare tumors tumors that that develop develop in in the the wall wall of of large large large blood blood blood vessels, vessels, vessels, thethe proximal proximal pulmonary pulmonary arteries arteries being being the the most most frequentfrequent frequent locationlocation location [[ 3535[35].].] . ThisThis This explainsex explainsplains that that thethe clinical clinical presentation presentationpresentation often oftenoften relates relatesrelates to to pulmonary pulmonary embolic embolic embolic disease, disease, disease, due due due to to tointravascular intravascular intravascu- tumorallartumoral tumoral spread. spread. spread. The The Theaorta aorta aorta is is the the is main themain main involved involved involved vessel vessel vessel of of the the of peripheral theperipheral peripheral circulation, circulation, circulation, and and intimalandintimal intimal sarcoma sarcoma sarcoma has has recently hasrecently recently been been been described described described to to be be to the the be most themost most frequ frequ frequententent primary primary primary cardiac cardiac cardiac sar- sar- comacoma [ 36[36].] .On On histology, histology, these these tumors tumors present present as as intraluminal intraluminal lesions lesions and and can can have have a a very very

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sarcoma [36]. On histology, these tumors present as intraluminal lesions and can have a veryheterogeneous, heterogeneous, non-distinctive non-distinctive phenotype. phenotype. The picture The picture ranges ranges from from a bland a bland spindle spindle cell cellproliferation proliferation to a tovery a very anaplastic anaplastic and andpleomorphic pleomorphic type typeof undifferentiated of undifferentiated sarcoma. sarcoma. The Thematrix matrix can be can collagenous, be collagenous, myxoid, myxoid, or can or caneven even show show lace- lace-likelike osteoid osteoid or chondroid or chondroid dif- differentiationferentiation (Figure (Figure 10). 10 Rarely). Rarely the the picture picture can can mimic mimic a aleiomyo leiomyo-,-, rhabdomy rhabdomy-,-, or or angiosar- angiosar- coma. There is no specificspecific immunohistochemicalimmunohistochemical marker,marker, butbut EGFREGFR andand nuclearnuclear MDM2MDM2 expression areare seenseen inin +/+/−− 70%70% of of cases cases ( (FigureFigure 10).10). Amplification Amplification of of the the 12q12 12q12-15-15 region, includingincluding CDK4 and MDM2 isis aa hallmarkhallmark andand isis oftenoften accompaniedaccompanied byby amplificationamplification andand activation of platelet-derivedplatelet-derived growth factorfactor alphaalpha (at(at 4q12)4q12) andand epidermalepidermal growthgrowth factorfactor receptorreceptor (at(at 7p11)7p11) [[35,3735,37].]. The prognosis is very poor, whichwhich relatesrelates toto thethe embolicembolic dissemination.dissemination. Lung metastasismetastasis isis seenseen inin aboutabout 40%40% ofof patients, patients, and and extrathoracic extrathoracic spread spread in in +/ +/−− 20%, includingincluding thethe brain,brain, skinskin andand lymphlymph nodes.nodes. Survival is rare beyondbeyond 33 yearsyears [[38,3938,39].].

Figure 10. Cont.

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Figure 10. Intimal sarcoma. Note the intravascular location (a), and the heterogeneous outlook of the tumor, ranging from Figure 10. Intimal sarcoma. Note the intravascular location (a), and the heterogeneous outlook of the tumor, ranging from bland spindled (b), to pleomorphic (c), to osteosarcoma-like (d). MDM2 expression is seen in (e). bland spindled (b), to pleomorphic (c), to osteosarcoma-like (d). MDM2 expression is seen in (e). 5. Low-Grade Osteosarcoma 5. Low-Grade Osteosarcoma Low-grade osteosarcomas are rare and are subdivided in parosteal and low-grade Low-grade osteosarcomas are rare and are subdivided in parosteal and low-grade central osteosarcoma. In both tumors, the diagnosis is often impossible in the absence of imagingcentral feature osteosarcoma.s, because they In often both look tumors, deceptively the diagnosis bland. Parosteal is often osteosarcoma impossible rep- in the absence resentsof imaging 4–5% of features,all osteosarcomas because and they is the often most look frequent deceptively surface bland.osteosarcoma. Parosteal It typi- osteosarcoma callyrepresents develops on 4–5% the ofposterior all osteosarcomas surface of the anddistal is femur the most of young frequent adults, surface mainly osteosarcoma.in the It thirdtypically decade. developsThe humerus on can the also posterior be rarely surface involved. of On the imaging, distal femur a heavily of mineralized young adults, mainly massin theattached third to decade. the cortex The is seen humerus (Figure can 11). also Histologically, be rarely involved.fascicles of Onnon imaging,-atypical a heavily spindlemineralized cells admixed mass with attached parallel to bone the cortextrabecula is seenare typical (Figure (Figure 11). 11). Histologically, In half of the fascicles of casesnon-atypical, cartilage islands spindle can cells be seen, admixed and about with half parallel of the tumors bone trabecula transgress are the typical cortex and (Figure 11). In invadehalf the of themedullary cases, cartilagecavity. Fifteen islands to 43% can dedifferentiate be seen, and into about a high half grade of the (osteo)sar- tumors transgress comathe [40 cortex]. Low and grade invade central the osteosarcoma medullary only cavity. accounts Fifteen for 1– to2% 43% of osteosarcomas dedifferentiate and into a high is mainly seen in the metaphysis of long bones, tibia and femur being most affected. This grade (osteo)sarcoma [40]. Low grade central osteosarcoma only accounts for 1–2% of tumor rarely involves jaw bones, axial and small tubular bones. Half of the cases occur in osteosarcomas and is mainly seen in the metaphysis of long bones, tibia and femur being the second to third decade. On imaging, a large lytic to mineralized mass is seen, often associatedmost affected. with focal This cortical tumor disruption, rarely involves which can jaw be bones, hard to axial see (Figure and small 12). On tubular histol- bones. Half ogy,of the the tumor cases consists occur in of the a fascicular second toand third moderately decade. cellular On imaging, fibroblastic a large proliferation, lytic to mineralized withmass minimal is seen, or no often atypia. associated The neopla withstic focalbone can cortical present disruption, as curved bone which trabeculae, can be hard to see mimicking(Figure fibrous12). On dysplasia, histology, or as the longitudinal tumor consists seams of ofbone, a fascicular as seen in parosteal and moderately osteo- cellular sarcomafibroblastic (Figure proliferation,12). Bone formation with can minimal even be orabsent, no atypia. resulting The in a neoplasticpicture that boneresem- can present blesas desmoplastic curved bone fibroma trabeculae, or low-grade mimicking fibrosarcoma. fibrous Very dysplasia, rarely dedifferentiation or as longitudinal can seams of occurbone, resulting as seen in ina classical parosteal high osteosarcoma-grade osteosarcoma (Figure-like 12 picture). Bone [41 formation]. Both tumors can evenhar- be absent, borresulting long marker in a or picture ring chromosomes that resembles with desmoplastic amplified 12q13 fibroma-15 regions, or low-grade including the fibrosarcoma. MDM2Very and rarely CDK4 dedifferentiation genes [42,43]. In can a high occur proportion resulting of in cases, a classical immunohistochemical high-grade osteosarcoma- MDM2like pictureand/or CDK4 [41]. expression Both tumors can harborbe found long as well. marker In this or respect, ring chromosomes search for MDM2 with amplified amplification/expression can be very useful to distinguish these low-grade sarcomas from 12q13-15 regions, including the MDM2 and CDK4 genes [42,43]. In a high proportion of their—often benign—mimics (Figures 11 and 12) [44]. The prognosis of both neoplasms is MDM2 CDK4 excellent,cases, immunohistochemicalwith 5-year survival rates of 90% and/orupon complete expressionresection. Chemotherapy can be found is as well. In onlythis administered respect, search in case fors ofMDM2 dedifferentiation,amplification/expression when the prognosis can is be that very of usefula conven- to distinguish tionalthese osteosarcoma. low-grade Inter sarcomasestingly, from when their—often low-grade central benign—mimics or parosteal osteosarcoma (Figures 11 de- and 12)[44]. differentiateThe prognosis into a high of both-grade neoplasms sarcoma, they is excellent,retain their withMDM2 5-year/CDK4 survival amplification rates and of 90% upon complete resection. Chemotherapy is only administered in cases of dedifferentiation, when the prognosis is that of a conventional osteosarcoma. Interestingly, when low- grade central or parosteal osteosarcoma dedifferentiate into a high-grade sarcoma, they retain their MDM2/CDK4 amplification and overexpression. In addition, the finding of MDM2 and/or CDK4 amplification/overexpression in a high-grade osteosarcoma indicates Diagnostics 2021, 11, x 11 of 16

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overexpression. In addition, the finding of MDM2 and/or CDK4 amplification/overexpression in a high-grade osteosarcoma indicates progression/dedifferentiation from a low- progression/dedifferentiationgrade osteosarcoma and practically fromexcludes a low-grade a primary conventional osteosarcoma high and-grade practically osteosar- excludes a coma [43]. primary conventional high-grade osteosarcoma [43].

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Figure 11. Parosteal osteosarcoma, typically presenting as a mineralized mass at the back of the Figure 11. Parosteal osteosarcoma, typically presenting as a mineralized mass at the back of the distal distal femur, X-ray (a), and whole mount section (b). At high power, the tumor consists of parallel femur,bone trabeculae X-ray (a and), and a typical whole spindle mount cell sectionproliferation (b). ( Atc). MDM2 high power, expression the is tumor present consists as well (d of). parallel bone trabeculae and a typical spindle cell proliferation (c). MDM2 expression is present as well (d).

Diagnostics 2021, 11, 496 12 of 15

Diagnostics 2021, 11, x 13 of 16

(a)

Diagnostics 2021, 11, x 14 of 16

FigureFigure 12. 12. LowLow-grade-grade central central osteosarcoma, osteosarcoma, showing showinga lytic lesion a lyticthe distal lesion femur the on distal X-ray femur (a). on X-ray (a). OnOn histology, histology, the the tumor tumor strongly strongly mimics mimics fibrous fibrous dysplasia, dysplasia, with the withvery irregular the very bone irregular trabecu- bone trabeculae laeembedded embedded in ine e fibrousfibrous stroma stroma (b (b). ).The The amplification amplification of the of MDM2 the MDM2 gene supportsgene supports the diagnosis the diagnosis (c). (c).

In conclusion, the story of MDM2 in sarcomas gives us insight into ‘M’olecular mechanisms. It has created a ‘D’iagnostic tool, FISH being more sensitive than immunohistochemistry. MDM2-amplified sarcomas ‘M’ay be druggable in the future. Finally, it helps us ‘TO’ sort out part of the numerous and complex sarcomas.

Funding: This research received no external funding. Acknowledgments: The author wishes to thank Maria Debiec-Rychter for supplying Figures 4 and 12c. Conflicts of Interest: The author declares no conflict of interest.

References 1. Momand, J.; Wu, H.H.; Dasgupta, G. MDM2-master regulator of the p53 tumor suppressosofier protein. Gene 2000, 242, 15–29 2. Cissé, M.Y.; Pyrdziak, S.; Firmin, N.; Gayte, L.; Heuillet, M.; Bellvert, F.; Fuentes Delpech, H.; Riscal, R.; Arena, G.; Chibon, F.; et al. Targeting MDM2-dependent serine metabolism as a therapeutic strategy for liposarcoma. Sci. Transl. Med. 2020, 12, 1–13 3. Dembla, V.; Somaiah, N.; Barata, P.; Hess, K.; Fu, S.; Janku, F.; Krap, D.D.; Naing, A.; Piha-Paul, S.A.; Subbiah, V.; et al. Preva- lence of MDM2 amplification and coalterations in 523 advanced cancer patients in the MD Anderson phase 1 clinic. Oncotarget 2018, 9, 33232–33243 4. Kato, S.; Ross, J.S.; Gay, L.; Dayyani, F.; Roszik, J.; Subbiah, V.; Kurzrock, R. Analysis of MDM2 Amplification: Next-Generation Sequencing of Patients With Diverse Malignancies. JCO Precis Oncol. 2018, 2, 1–14. 5. Kommoss, F.E.K.F.; Chang, K.T.E.; Stichel, D.; Banito, A.; Jones, D.T.W.; Heilig, C.E.; Fröhling, S.; Sahm, F.; Stenzinger, A.; Hartmann, W.; et al. Endometrial stromal sarcomas with BCOR-rearrangement harbor MDM2 amplifications. J. Pathol. Clin. Res. 2020, 6, 178–184 6. Biswas, S.; Killick, E.; Jochemsen, A.G.; Lunec, J. The clinical development of p53-reactivating drugs in sarcomas-charting future therapeutic approaches and understanding the clinical molecular toxicology of Nutlins. Expert Opin. Investig. Drugs 2014, 23, 629–645 7. Li, Q.; Zhang, Y.; El-Naggar, A.; Xiong, S.; Yang, P.; Jackson, J.G.; Chau, G.; Lozano, G. Therapeutic Efficacy of p53 Restoration in Mdm25-Overexpressing Tumors. Mol Cancer Res. 2014, 12, 901–911 8. Obrador-Hevia, A.; Martinez-Font, E.; Felipe-Abrio, I.; Calabuig-Fariňas Serra-Sitjar, M.; Lόpez-Guerrero, J.A.; Ramos, R.; Ale- many, R.; Martĭn-Broto, J. RG7112, a Small-Molecule Inhibitor of MDM2, Enhances Trabectedin Response in Soft Tissue Sarco- mas. Cancer Investig. 2015, 33, 440–450 9. Bill, K.L.; Garnett, J.; Meaux, I.; Ma, X.Y.; Bolshakov, S.; Creighton, C.J.; Barriere, C.; Dubusche, L.; Lazar, A.; Prudner, B.C.; et al. SAR405838: A novel and potent inhibitor of the MDM2:p53 axis for the treatment of dedifferentiated liposarcoma. Clin. Cancer Res. 2015, epub ahead of print. 10. Cornillie, J.; Wozniak, A.; Li, H.; Gebreyohannes, Y.K.; Wellens, J.; Hompes, D.; Debiec-Rychter, M.; Sciot, R.; Schöffski, P. Anti- tumor activity of the MDM2-TP53 inhibitor BI-907828 in dedifferentiated liposarcoma patient-derived xenograft models harboring MDM2 amplification. Clin. Transl. Oncol. 2020, 22, 546–554, doi:10.1007/s12094-019-02158-z

Diagnostics 2021, 11, 496 13 of 15

In conclusion, the story of MDM2 in sarcomas gives us insight into ‘M’olecular mechanisms. It has created a ‘D’iagnostic tool, FISH being more sensitive than immunohistochemistry. MDM2-ampliﬁed sarcomas ‘M’ay be druggable in the future. Finally, it helps us ‘TO’ sort out part of the numerous and complex sarcomas.

Funding: This research received no external funding. Acknowledgments: The author wishes to thank Maria Debiec-Rychter for supplying Figures4 and 12c. Conﬂicts of Interest: The author declares no conﬂict of interest.

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