Myxoid pleomorphic liposarcoma of the orbit: intratumoural genetic similarities and heterogeneity

To the Editor, Malignant adipocytic neoplasms are rare in the paediatric population, in contrast to adults. An exception is the recently described entity myxoid pleomorphic liposarcoma (MPL), which occurs mostly in the mediastinum of children and young adults. First described in 2009, it is an exceptionally rare tumour characterised histologically by a combination of myxoid liposarcoma-like and pleomorphic liposarcoma-like areas.1Alaggio R. Coffin C.M. Weiss S.W. et al.Liposarcomas in young patients: a study of 82 cases occurring in patients younger than 22 years of age.Am J Surg Pathol. 2009; 33: 645-658Crossref PubMed Scopus (157) Google Scholar,2WHO Classification of Tumours Editorial BoardWHO Classification of Tumours of Soft Tissue and Bone. IARC Press, Lyon2020Google Scholar It has a very aggressive clinical course with high rates of metastases, and there is currently no standard treatment regimen for this tumour.1Alaggio R. Coffin C.M. Weiss S.W. et al.Liposarcomas in young patients: a study of 82 cases occurring in patients younger than 22 years of age.Am J Surg Pathol. 2009; 33: 645-658Crossref PubMed Scopus (157) Google Scholar,2WHO Classification of Tumours Editorial BoardWHO Classification of Tumours of Soft Tissue and Bone. IARC Press, Lyon2020Google Scholar We herein report the second case of an MPL occurring in the orbit, an extramediastinal site, and demonstrate both genomic similarities as well as heterogeneity in both myxoid liposarcoma-like and pleomorphic liposarcoma-like areas using microarray-based whole genome copy number analysis. A 12-year-old female patient presented with a 3-month history of a gradually enlarging right orbital mass. The mass was firm, erythematous, and caused proptosis of the globe. A computed tomography (CT) scan showed a 4.9×4.1×2.9 cm, well circumscribed, hypodense mass within the right orbit displacing the globe superiorly and anteriorly. No bone destruction or distant metastasis was detected at presentation. The patient underwent an orbitotomy with piecemeal excision of the mass. Neoadjuvant chemoradiotherapy was initiated promptly after tissue biopsy. Oncological review revealed no personal or family history of cancers to suggest Li–Fraumeni syndrome. A subsequent repeat CT scan at 2 months post-surgery showed progression of the tumour. The tumour had increased in size, and now infiltrated the extra-ocular muscles with entrapment of the optic nerve. Following repeated bacterial infections due to chemotherapy toxicity, the patient was terminally discharged 2 years after presentation. Histological examination showed a liposarcoma with distinct myxoid and pleomorphic areas. The myxoid areas bore a close histological resemblance to myxoid liposarcoma; these areas were of low to moderate cellularity and comprised spindled to ovoid tumour cells with mild to moderate nuclear atypia within an abundant myxoid matrix. Pulmonary oedema-like microcystic spaces and scattered uni-to multi-vacuolated lipoblasts were present. A fine arborising vasculature was seen focally (Fig. 1A–C). These myxoid areas merged with high-grade pleomorphic areas comprising cellular sheets of epithelioid, spindled and bizarre appearing cells with marked nuclear atypia, including multi-nucleated tumour giant cells. (Fig. 1D,E). Some of these bizarre cells also contained multi-vacuolated cytoplasm, resembling pleomorphic lipoblasts (Fig. 1E). Mitotic activity exceeded 20 per 10 high power fields. On immunohistochemistry, the tumour cells showed patchy expression of S100, and intracytoplasmic lipid vacuoles were highlighted with adipophilin (Fig. 1F). A null pattern of p53 expression was observed, and there was no expression of CD34, desmin, myogenin, myoD1, and CD117. INI-1 expression was retained. Molecular studies were performed. Fluorescence in situ hybridisation (FISH) studies showed no evidence of DDIT3 rearrangement or MDM2 gene amplification. OncoScan whole genome copy number microarray-based assay (ThermoFisher Scientific, USA) was performed separately on both the myxoid and pleomorphic areas. Both areas showed complex chromosomal alterations with more similarities than differences between the two (Fig. 2). Copy number alterations found in both areas included amplifications of chromosomes 1, 2, 7, 12, 19, 20, 21, segmental gains in chromosomes 3p36.3p25.1, 5p15.3p13.1, 10p, loss of heterozygosity (LOH) in chromosomes 3, 4, 5q, 6, 11, 14, 15, 16, 17 and 18, and MYC, CEBPA and CCNE1 gene amplifications. Genetic differences were also observed. The myxoid area showed gains of chromosome segments 3p25.1p22.3, 5q11.1q22.1, 6q, 10q and loss of chromosome segment 14q11.2q24.3. These copy number variants were not observed in the pleomorphic area. Small gains and losses in 6p were observed in the pleomorphic area only. The 13q14 region containing the RB1 gene showed no loss in both myxoid and pleomorphic areas. MPL is a newly described and rare paediatric tumour which occurs most commonly in the mediastinum.1Alaggio R. Coffin C.M. Weiss S.W. et al.Liposarcomas in young patients: a study of 82 cases occurring in patients younger than 22 years of age.Am J Surg Pathol. 2009; 33: 645-658Crossref PubMed Scopus (157) Google Scholar, 2WHO Classification of Tumours Editorial BoardWHO Classification of Tumours of Soft Tissue and Bone. IARC Press, Lyon2020Google Scholar, 3Creytens D. Folpe A.L. Koelsche C. et al.Myxoid pleomorphic liposaroma - a clinicopathologic, immunohistochemical, molecular genetic and epigenetic study of 12 cases, suggesting a possible relationship with conventional pleomorphic liposarcoma.Mod Pathol. 2021; 34: 2043-2049Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar, 4Dermawan J.K. Hwang S. Wexler L. et al.Myxoid pleomorphic liposarcoma is distinguished from other liposarcomas by widespread loss of heterozygosity and significantly worse overall survival: a genomic and clinicopathologic study.Mod Pathol. 2022; 35: 1644-1655Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar, 5Peng R. Li N. Lan T. et al.Liposarcoma in children and young adults: a clinicopathologic and molecular study of 23 cases in one of the largest institutions of China.Virchows Arch. 2021; 479: 537-549Crossref PubMed Scopus (9) Google Scholar Rare cases occurring in extramediastinal sites have been reported, involving the lower extremities and the head and neck region, including one previous case in the orbit.1Alaggio R. Coffin C.M. Weiss S.W. et al.Liposarcomas in young patients: a study of 82 cases occurring in patients younger than 22 years of age.Am J Surg Pathol. 2009; 33: 645-658Crossref PubMed Scopus (157) Google Scholar,3Creytens D. Folpe A.L. Koelsche C. et al.Myxoid pleomorphic liposaroma - a clinicopathologic, immunohistochemical, molecular genetic and epigenetic study of 12 cases, suggesting a possible relationship with conventional pleomorphic liposarcoma.Mod Pathol. 2021; 34: 2043-2049Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar, 4Dermawan J.K. Hwang S. Wexler L. et al.Myxoid pleomorphic liposarcoma is distinguished from other liposarcomas by widespread loss of heterozygosity and significantly worse overall survival: a genomic and clinicopathologic study.Mod Pathol. 2022; 35: 1644-1655Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar, 5Peng R. Li N. Lan T. et al.Liposarcoma in children and young adults: a clinicopathologic and molecular study of 23 cases in one of the largest institutions of China.Virchows Arch. 2021; 479: 537-549Crossref PubMed Scopus (9) Google Scholar, 6Francom C.R. Leoniak S.M. Lovell M.A. et al.Head and neck pleomorphic myxoid liposarcoma in a child with Li-Fraumeni syndrome.Int J Pediatr Otorhinolaryngol. 2019; 123: 191-194Crossref PubMed Scopus (18) Google Scholar The histomorphological features of the tumour in our case are congruent with previously described cases, with myxoid liposarcoma-like areas transitioning to pleomorphic liposarcoma-like areas. Importantly, it lacks both the FUS/EWSR1-DDIT3 gene fusions seen in conventional myxoid liposarcoma, as well as the MDM2 amplification present in dedifferentiated liposarcoma.1Alaggio R. Coffin C.M. Weiss S.W. et al.Liposarcomas in young patients: a study of 82 cases occurring in patients younger than 22 years of age.Am J Surg Pathol. 2009; 33: 645-658Crossref PubMed Scopus (157) Google Scholar,2WHO Classification of Tumours Editorial BoardWHO Classification of Tumours of Soft Tissue and Bone. IARC Press, Lyon2020Google Scholar The genetic findings seen in our tumour are also consistent with recent studies on the molecular characteristics of MPL. Genome-wide LOH in a hyperdiploid genome has been reported to be a distinct genomic feature of MPL that may help distinguish it from other liposarcoma subtypes.4Dermawan J.K. Hwang S. Wexler L. et al.Myxoid pleomorphic liposarcoma is distinguished from other liposarcomas by widespread loss of heterozygosity and significantly worse overall survival: a genomic and clinicopathologic study.Mod Pathol. 2022; 35: 1644-1655Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar,7Hofvander J. Jo V.Y. Ghanei I. et al.Comprehensive genetic analysis of a paediatric pleomorphic myxoid liposarcoma reveals near-haploidization and loss of the RB1 gene.Histopathology. 2016; 69: 141-147Crossref PubMed Scopus (42) Google Scholar Indeed, we observed widespread LOH across multiple chromosomes in this case, which also showed predominantly copy number gains rather than losses. As previously suggested, this unusual pattern of copy number alterations (possibly derived from a near-haploid clone) is reminiscent of the genetic changes reported in some cases of inflammatory leiomyosarcomas, which can show a near-haploid genotype, with or without subsequent whole-genome doubling.4Dermawan J.K. Hwang S. Wexler L. et al.Myxoid pleomorphic liposarcoma is distinguished from other liposarcomas by widespread loss of heterozygosity and significantly worse overall survival: a genomic and clinicopathologic study.Mod Pathol. 2022; 35: 1644-1655Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar,8Arbajian E. Koster J. Vult von Steyern F. et al.Inflammatory leiomyosarcoma is a distinct tumor characterized by near-haploidization, few somatic mutations, and a primitive myogenic gene expression signature.Mod Pathol. 2018; 31: 93-100Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar In addition, multiple chromosomal gains with recurrent amplifications of chromosomes 1, 19 and 21,3,4 recurrent MYC, CEBPA and CCNE1 gene amplifications,4Dermawan J.K. Hwang S. Wexler L. et al.Myxoid pleomorphic liposarcoma is distinguished from other liposarcomas by widespread loss of heterozygosity and significantly worse overall survival: a genomic and clinicopathologic study.Mod Pathol. 2022; 35: 1644-1655Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar TP53 mutations4Dermawan J.K. Hwang S. Wexler L. et al.Myxoid pleomorphic liposarcoma is distinguished from other liposarcomas by widespread loss of heterozygosity and significantly worse overall survival: a genomic and clinicopathologic study.Mod Pathol. 2022; 35: 1644-1655Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar,5Peng R. Li N. Lan T. et al.Liposarcoma in children and young adults: a clinicopathologic and molecular study of 23 cases in one of the largest institutions of China.Virchows Arch. 2021; 479: 537-549Crossref PubMed Scopus (9) Google Scholar and loss of RB1 have been previously reported.3Creytens D. Folpe A.L. Koelsche C. et al.Myxoid pleomorphic liposaroma - a clinicopathologic, immunohistochemical, molecular genetic and epigenetic study of 12 cases, suggesting a possible relationship with conventional pleomorphic liposarcoma.Mod Pathol. 2021; 34: 2043-2049Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar, 4Dermawan J.K. Hwang S. Wexler L. et al.Myxoid pleomorphic liposarcoma is distinguished from other liposarcomas by widespread loss of heterozygosity and significantly worse overall survival: a genomic and clinicopathologic study.Mod Pathol. 2022; 35: 1644-1655Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar, 5Peng R. Li N. Lan T. et al.Liposarcoma in children and young adults: a clinicopathologic and molecular study of 23 cases in one of the largest institutions of China.Virchows Arch. 2021; 479: 537-549Crossref PubMed Scopus (9) Google Scholar,7Hofvander J. Jo V.Y. Ghanei I. et al.Comprehensive genetic analysis of a paediatric pleomorphic myxoid liposarcoma reveals near-haploidization and loss of the RB1 gene.Histopathology. 2016; 69: 141-147Crossref PubMed Scopus (42) Google Scholar In a recent study of MPLs, MYC amplifications were reported in 25% of MPLs, while CEBPA and CCNE1 amplifications were reported in 38% of MPLs.4Dermawan J.K. Hwang S. Wexler L. et al.Myxoid pleomorphic liposarcoma is distinguished from other liposarcomas by widespread loss of heterozygosity and significantly worse overall survival: a genomic and clinicopathologic study.Mod Pathol. 2022; 35: 1644-1655Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar MYC, CEBPA, and CCNE1 amplifications were found rarely in pleomorphic liposarcomas.4Dermawan J.K. Hwang S. Wexler L. et al.Myxoid pleomorphic liposarcoma is distinguished from other liposarcomas by widespread loss of heterozygosity and significantly worse overall survival: a genomic and clinicopathologic study.Mod Pathol. 2022; 35: 1644-1655Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar In our case, we observed amplifications of chromosomes 1, 19 and 21 (along with other chromosomal gains), as well as MYC, CEBPA and CCNE1 gene amplifications. RB1 gene deletion, which has been reported in a subset of MPLs, was not detected in this tumour. Interestingly, genomic features of both the myxoid and pleomorphic areas were more similar than different, despite their obvious histomorphological differences. Both areas showed a complex copy number alteration profile with widespread LOH and overlaps in amplified chromosomal regions. These findings argue against the notion of MPL being a dedifferentiated tumour or mixed tumour, and instead suggest that the varied morphological features are likely a consequence of underlying genomic instability. Both somatic and germline TP53 mutations (Li–Fraumeni syndrome) have been reported in MPLs.4Dermawan J.K. Hwang S. Wexler L. et al.Myxoid pleomorphic liposarcoma is distinguished from other liposarcomas by widespread loss of heterozygosity and significantly worse overall survival: a genomic and clinicopathologic study.Mod Pathol. 2022; 35: 1644-1655Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar, 5Peng R. Li N. Lan T. et al.Liposarcoma in children and young adults: a clinicopathologic and molecular study of 23 cases in one of the largest institutions of China.Virchows Arch. 2021; 479: 537-549Crossref PubMed Scopus (9) Google Scholar, 6Francom C.R. Leoniak S.M. Lovell M.A. et al.Head and neck pleomorphic myxoid liposarcoma in a child with Li-Fraumeni syndrome.Int J Pediatr Otorhinolaryngol. 2019; 123: 191-194Crossref PubMed Scopus (18) Google Scholar,9Sinclair T.J. Thorson C.M. Alvarez E. et al.Pleomorphic myxoid liposarcoma in an adolescent with Li-Fraumeni syndrome.Pediatr Surg Int. 2017; 33: 631-635Crossref PubMed Scopus (32) Google Scholar,10Zare S.Y. Leivo M. Fadare O. Recurrent pleomorphic myxoid liposarcoma in a patient with Li-Fraumeni syndrome.Int J Surg Pathol. 2020; 28: 225-228Crossref PubMed Scopus (14) Google Scholar The presence of TP53 mutations is often associated with genomic instability and intra-tumoural heterogeneity.11Raynaud F. Mina M. Tavernari D. et al.Pan-cancer inference of intra-tumor heterogeneity reveals associations with different forms of genomic instability.PLoS Genet. 2018; 14e1007669Crossref PubMed Scopus (63) Google Scholar In our case, p53 showed a null pattern of staining on immunohistochemistry, raising the possibility of an underlying TP53 mutation. A key differential diagnosis of MPL is pleomorphic liposarcoma with myxoid or myxofibrosarcoma-like areas, which is also associated with overall poor survival. In addition to morphological similarities, both tumours show complex chromosomal alterations. Furthermore, TP53 and RB1 mutations can also be seen in pleomorphic liposarcomas.12Ghadimi M.P. Liu P. Peng T. et al.Pleomorphic liposarcoma: clinical observations and molecular variables.Cancer. 2011; 117: 5359-5369Crossref PubMed Scopus (87) Google Scholar Clinically, pleomorphic liposarcomas occur mostly in elderly patients rather than in children, and usually in the extremities.2WHO Classification of Tumours Editorial BoardWHO Classification of Tumours of Soft Tissue and Bone. IARC Press, Lyon2020Google Scholar Widespread LOH, seen in MPL, may be useful in helping to differentiate between the two entities for cases with unusual clinicopathological features.4Dermawan J.K. Hwang S. Wexler L. et al.Myxoid pleomorphic liposarcoma is distinguished from other liposarcomas by widespread loss of heterozygosity and significantly worse overall survival: a genomic and clinicopathologic study.Mod Pathol. 2022; 35: 1644-1655Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar In summary, we have presented the second reported case of the rare entity MPL occurring in the orbit, an extra-mediastinal site. Morphologically distinct areas of the tumour showed similarly complex copy number alteration profiles that include widespread LOH and amplifications, with minor intra-tumoural heterogeneity. Accurate diagnosis and recognition of this entity is essential for further studies on treatment strategies for this highly aggressive tumour associated with a poor prognosis. Written informed consent was obtained from the patient for publication of this case report and any accompanying images. This study was funded by the VIVA Foundation for Children with Cancer. The authors state that there are no conflicts of interest to disclose.