A thoracic wall lipoblastoma in a 3-month-old infant: A case report and review of the literature

Lipoblastoma is a rare benign tumor of adipose tissue seen almost always in infancy and early childhood. Lipoblastoma is present in 2 forms which are pathologically identical: circumscribed and diffuse. It is typically located in the extremities, and less frequently in head-neck region, trunk, and various organs. Lipoblastoma is a tumor with good prognosis with no reported metastases, despite its potential for local invasion and rapid growth. Our patient was a 3-month-old boy who was brought to our clinic for rapidly growing mass in the right hemithorax. With the aim of both diagnosis and treatment, the lipomatous mass was removed by local resection. In addition to the patient's age, histologic and cytogenetic analyses assisted the diagnosis of diffuse lipoblastoma. In the postoperative period, the thorax wall was unaffected, and after 6 years of follow-up no recurrence was observed. In the English literature, 8 cases of thoracic wall lipoblastoma have been previously reported, and only 3 of diffuse form. Here, we report, at our knowledge, the fourth case of thoracic diffuse lipoblastoma, in which cytogenetic analysis showed a previously undescribed karyotype aberration involving chromosomes 8, 13, and 16.

Cutaneous lipoma in children: 5 cases with Bannayan-Riley-Ruvalcaba syndrome

Cutaneous lipoma is rare in children, but it can be part of a syndrome such as the Bannayan-Riley-Ruvalcaba syndrome (BRRS). The BRRS is a dominant autosomal disorder characterized by cutaneous lipomas, macrocephaly, intestinal polyps, and developmental delay associated with PTEN gene mutations. This syndrome is thought to represent a pediatric form of the Cowden syndrome, characterized among other features by an increased risk of cancer. We report 5 cases of BRRS, all diagnosed in children with lipoma and macrocephaly. Children presenting with lipomas need a complete physical examination to look for other signs of BRRS, because they may need further follow-up for tumor screening in adulthood.

Lipoblastoma and lipoblastomatosis

We report two cases of lipoblastoma of the buttock in a 10-month-old boy and a 20-month-old girl, the first with rearrangement of chromosome 8 and the second without cytogenetic abnormality, and one case of lipoblastomatosis of a leg in a 6-month-old boy with a normal karyotype but with a rearrangement of the PLAG1 gene. Lipoblastoma and lipoblastomatosis are two different presentation of the same rare benign soft tissue mesenchymal tumour arising from fetal white fat and occurring almost exclusively in young children under 3 years. These neoplasms have no malignant potential but may recur in cases of incomplete resection. Histological diagnosis sometimes used to be difficult because of the close resemblance of the lesion with myxoïd liposarcoma. Nowadays, cytogenetic analysis may contribute to the diagnosis by showing abnormalities of the long arm of chromosome 8, leading to rearrangement of the PLAG1 gene. Actual advances in cytogenetic molecular analysis may aid in accurate diagnosis.

The value of MDM2 and CDK4 amplification levels using real-time polymerase chain reaction for the differential diagnosis of liposarcomas and their histologic mimickers

Atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDL) and dedifferentiated liposarcoma (DDL) are reported to have murine double-minute type 2 (MDM2) and cyclin-dependent kinase 4 (CDK4) amplification as a characteristic genetic alteration. To evaluate the diagnostic utility of this gene abnormality, we analyzed 19 liposarcomas, 21 malignant fibrous histiocytomas, 3 leiomyosarcomas, 5 malignant peripheral nerve sheath tumors, 23 lipomas, and 28 nonneoplastic fat tissues using real-time polymerase chain reaction (PCR) and fluorescence in situ hybridization (FISH). In real-time PCR, all ALT/WDLs and DDLs had both MDM2 and CDK4 amplifications. The amplification levels in ALT/WDLs and DDLs were significantly higher than those in the other sarcomas, lipomas, and nonneoplastic fat tissues (P < .05); however, those in the other sarcomas and lipomas were not significantly higher than those in nonneoplastic tissues. In FISH, all ALT/WDLs and DDLs had both MDM2 and CDK4 amplifications, and all of the myxoid/round cell liposarcomas, leiomyosarcomas, malignant peripheral nerve sheath tumors, and all but one of the malignant fibrous histiocytomas did not have the amplifications. In this study, MDM2 and CDK4 amplifications were confirmed in ALT/WDLs and DDLs, and the amplification levels were significantly higher than those in the other tumors. An analysis of MDM2 and CDK4 amplification using real-time PCR, as well as FISH, is useful for the differential diagnosis of liposarcomas and their histologic mimickers.

Surgical management of lipoblastoma

BACKGROUND/PURPOSE

Lipoblastoma/lipoblastomatosis, a rare benign pediatric tumor composed of embryonic fat, most often presents as a rapidly growing mass in children younger than 3 years. This benign tumor locally recurs up to 25% of the time. This retrospective review was done to emphasize problems with diagnosis, management, and the approach to follow-up care.

METHODS

Sixteen cases of pathologically proven lipoblastoma presenting to a single institution over a 16-year period (1988-2004) were reviewed retrospectively for clinical features and outcome.

RESULTS

There were 11 males and 5 females ranging in age from 18 days to 12.75 years. Preoperative diagnoses were accurate in only 3 cases. Two lesions recurred locally over a period of 10 months and 5 years. One lesion presented with local infiltration. Six lesions were right-sided, 5 were left-sided, and 5 were midline.

CONCLUSIONS

It is important to consider lipoblastoma in the diagnosis of a rapidly enlarging fatty mass in children. Complete resection is the only definitive treatment and should not be delayed when impingement on surrounding structures is imminent. There is a tendency for these lesions to recur despite presumed complete excision. Therefore, follow-up for a minimum of 5 years is recommended.

Extramammary myofibroblastoma is genetically related to spindle cell lipoma

Extramammary-type myofibroblastoma is a rare, benign spindle cell lesion, strictly resembling the breast counterpart, but occurring in extramammary sites, mainly in the inguinal/groin area. In this paper, we describe an extramammary-type myofibroblastoma in the groin of a 37-year-old male patient. The tumor showed a typical morphological and immunophenotypical profile, including staining for both CD34 and desmin. Dual-color interphase florescent in situ hybridization analysis revealed losses of RB/13q14 and FKHR/13q14 loci within tumor cells. The chromosome 13 rearrangements associated with the loss of the 13q14 chromosomal region are typically seen in spindle cell lipoma, and have been previously recognized in mammary myofibroblastoma, providing strong evidence for a pathogenetic link between these lesions.

MRI characteristics of parosteal lipomas associated with the HMGA2-LPP fusion gene

BACKGROUND

The magnetic resonance (MR) characteristics of parosteal lipomas with the HMGA2-LPP fusion transcripts are described.

PATIENTS AND METHODS

The expression of HMGA2-LPP fusion transcripts was determined using the reverse transcription-polymerase chain reaction method.

RESULTS

MR images of two cases with the fusion transcripts, a 56-year-old man and a 50-year-old woman, revealed heterogeneous high signal intensities on T1- and T2-weighted images, showing heterogeneous curvilinear enhancement on fat-suppressed T1-weighted images after Gd-DTPA injection, which resembled those of well-differentiated liposarcomas.

CONCLUSION

Since the HMGA2-LPP fusion transcripts are exclusively detectable in benign mesenchymal tumors, testing HMGA2-LPP expression may be useful for differential diagnosis in cases of radiologically-suspected well-differentiated liposarcomas.

Truncation and fusion of HMGA2 in lipomas with rearrangements of 5q32-->q33 and 12q14-->q15

Chromosome segment 12q13-->q15 recombines with many different chromosome bands in lipomas and at least ten recurrent translocations have been identified. The HMGA2 gene is often rearranged, but little is known about the molecular consequences at other breakpoints. Fusion genes between HMGA2 (12q14-->q15) and LPP (3q27-->q28), LHFP (13q12) and CMKOR1 (2q37) have been reported. In the present study, eight lipomas with rearrangements involving chromosome bands 12q14-->q15 and 5q32-->q33 were analyzed. In chromosome 5, five of the cases had a breakpoint in the 5' part of EBF in 5q33, while three cases had breakpoints located about 200 kb 3' of EBF. In chromosome 12, the breakpoints clustered to the region of HMGA2. Four cases had breaks within the gene and four had breaks 5' to HMGA2 where the gene BC058822 is located. Two versions of an HMGA2/EBF fusion transcript were detected in one case; one transcript was in frame and the other out of frame. Identical EBF/BC058822 fusion transcripts, seen in two cases, one of which also had the HMGA2/EBF transcript, were out of frame and resulted in truncation of EBF. Since EBF and HMGA2 have different orientations, the findings must be explained by complex aberrations including multiple breaks. The combined data indicate that the pathogenetically significant event is fusion, truncation or transcriptional activation of HMGA2, but it can not be excluded that EBF, which has been implicated in adipogenesis, contributes to the tumor development.

Rearrangement of chromosomal region 8q11-13 in lipomatous tumours: correlation with lipoblastoma morphology

Cytogenetics is of considerable value when diagnosing lipomatous tumours, as different tumour types have different more or less specific chromosomal abnormalities. One such entity is lipoblastoma, which is a benign lipomatous tumour that often exhibits rearrangements of chromosome bands 8q11-13, and the gene PLAG1 has been implicated as the target of these chromosomal changes. All lipomatous tumours karyotyped at the Norwegian Radium Hospital were reviewed, looking for rearrangements of 8q11-13. Five tumours exhibiting chromosomal abnormalities affecting this region were found. Only one of them was morphologically diagnosed as a lipoblastoma, two being classified as lipomas, one as a hibernoma, and one as a well-differentiated liposarcoma. The two tumours successfully analysed with bacterial artificial chromosomes (BACs) covering the gene PLAG1 showed involvement of this gene in the rearrangement. The findings raise the question as to what extent the diagnosis lipoblastoma should be based on histopathological or cytogenetic/molecular data or a combination thereof. When karyotypic information from this series was combined with available literature data, it was found that the sensitivity of 8q11-13 rearrangements for diagnosing lipoblastomas when found in a lipomatous tumour was 77% and that the corresponding specificity was 98%. The validity of these calculations of the diagnostic information provided by the cytogenetic findings is, of course, totally dependent on the morphological diagnosis made in each case. Regardless of what the precise phenotypic diagnosis was, it is suggested that lipomatous tumours with 8q11-13 rearrangement constitute a distinct pathogenetic entity. When selective therapies tailor-made against the specific pathogenetic rearrangement become available, it will become mandatory to pay more attention to the genetic constitution of the tumour cells than to their phenotypic appearance.

Overexpression of HMGA2-LPP fusion transcripts promotes expression of the alpha 2 type XI collagen gene

In a subset of human lipomas, a specific t(3;12) chromosome translocation gives rise to HMGA2-LPP fusion protein, containing the amino (N)-terminal DNA binding domains of HMGA2 fused to the carboxyl (C)-terminal LIM domains of LPP. In addition to its role in adipogenesis, several observations suggest that HMGA2-LPP is linked to chondrogenesis. Here, we analyzed whether HMGA2-LPP promotes chondrogenic differentiation, a marker of which is transactivation of the alpha 2 type XI collagen gene (Col11a2). Real-time PCR analysis showed that HMGA2-LPP and COL11A2 were co-expressed. Luciferase assay demonstrated that either of HMGA2-LPP, wild-type HMGA2 or the N-terminal HMGA2 transactivated the Col11a2 promoter in HeLa cells, while the C-terminal LPP did not. RT-PCR analysis revealed that HMGA2-LPP transcripts in lipomas with the fusion were 591-fold of full-length HMGA2 transcripts in lipomas without the fusion. These results indicate that in vivo overexpression of HMGA2-LPP promotes chondrogenesis by upregulating cartilage-specific collagen gene expression through the N-terminal DNA binding domains.

Fusion of the HMGA2 and NFIB genes in lipoma

The major cytogenetic subgroup of lipomas is characterized by aberrations of chromosome segment 12q13-15, which recombines with a large number of other chromosomal regions. The gene HMGA2 is the main target in these aberrations. For some recurrent rearrangements, chimeric transcripts, including the 5' part of HMGA2, have been described. The 3' partners identified are LPP, LHFP, CMKOR1, and EBF. In addition, subsets of other benign solid tumors show aberrations of 12q13-15. Among pleomorphic adenomas of the salivary glands, where the preferred recombination partner with 12q13-15 is 9p22-24, an HMGA2/NFIB fusion gene has been reported. In the present study, two cases of lipoma with rearrangements of 9p22-24 and 12q15 were analyzed by reverse transcription polymerase chain reaction to find out if HMGA2/NFIB was also present in lipoma. An in-frame fusion transcript, combining the four first exons of HMGA2 with exon 8 of NFIB, was detected in one case. It was identical to a transcript that was previously described in salivary gland adenoma and contained a stop codon shortly 3' of the fusion point. The finding of the same fusion gene in different tumors is not unique. For example, HMGA2/LPP has been reported in lipoma, pulmonary chondroid hamartoma, and soft tissue chondroma. Since similar 9;12 translocations have been described also in rare cases of hamartoma and uterine leiomyoma, the occurrence of HMGA2/NFIB could be postulated in these tumors as well.

Transactivation functions of the tumor-specific HMGA2/LPP fusion protein are augmented by wild-type HMGA2

The gene encoding the architectural transcription factor HMGA2 is frequently rearranged in several benign tumors of mesenchymal origin. The lipoma preferred partner (LPP) gene is the most frequent translocation partner of HMGA2 in a subgroup of lipomas, which are benign tumors of adipose tissue. In these lipomas, HMGA2/LPP fusion transcripts are expressed, which encode for the three AT-hooks of HMGA2 followed by the two most carboxyl-terminal LIM domains (protein-protein interaction domains) of LPP. Identical fusion transcripts are also expressed in other benign mesenchymal tumors. Previous studies revealed that the LIM domains of LPP have transcriptional activation capacity in GAL4-based luciferase reporter assays. Here, we show that the HMGA2/LPP fusion protein retains the transactivation functions of the LPP LIM domains and thus functions as transcription factor. The HMGA2/LPP fusion protein activates transcription from the well-characterized PRDII element, which is a part of the IFN-beta enhancer and which is known to bind to HMGA2. We also show that HMGA2/LPP activates transcription from the BAT-1 element of the rhodopsin promoter, a HMGA1-binding element. HMGA1 is a closely related family member of HMGA2. Finally, in a number of lipomas, HMGA2/LPP and HMGA2 are coexpressed, and HMGA2 augments the transactivation functions of HMGA2/LPP. These results support the concept that the transactivation functions of the novel HMGA2/LPP transcription factor contribute to lipomagenesis.

Differential gene expression in liposarcoma, lipoma, and adipose tissue

Malignant transformation is thought to be associated with changes in the expression of a number of genes, and this alteration in gene expression is felt to be critical to the development of the malignant phenotype. Sarcomas represent a diverse group of tumors derived from cells of mesenchymal origin. Marked heterogeneity exists in the biological behavior of sarcomas, even within histologic subtypes of sarcomas. In an effort to better understand the biology of liposarcomas, gene expression in normal adipose tissue, lipomas, and liposarcomas was examined using the Affymetrix microarray technology. Differences in gene expression were quantified as the fold change in gene expression among the sample sets. Differences in gene expression among normal adipose tissue, lipomas, and liposarcomas were observed. In addition, genes expressed uniquely in liposarcoma among these and 18 other tissue sample sets were identified. Gene sets were devised that allowed the separation of liposarcomas from other samples, and most normal adipose tissue from most lipomas using the Eisen clustering software "Cluster." We conclude that differences in gene expression can be identified among different tumors derived from the adipocyte series. Such differences in gene expression may help differentiate among subtypes of sarcomas, and may also yield clues to the pathophysiology of this heterogeneous group of tumors.

Atypical lipomatous tumor with rare structural rearrangements involving chromosomes 8 and 12

Atypical lipomatous tumor (ALT), an intermediate malignant neoplasm of soft tissues, is characterized by the presence of supernumerary ring and giant marker chromosomes. These supernumerary chromosomes consistently contain amplified 12q-material in association with amplified segments from a variety of other chromosomes. However, a few cases of ALT with other types of chromosomal rearrangements have been reported earlier. We report on new types of structural aberrations in a case of ALT. In a pseudodiploid karyotype, there were two aberrant chromosomes, both consisting of alternating chromosome 8 and 12 sequences as shown by multicolor fluorescence in situ hybridization (FISH). The complex rearrangement was not only the result of multiple breaks and reunions of these chromosomes, but was also associated with a gain of chromosome 12 sequences. FISH analyses revealed that the number of MDM2 signals was slightly elevated (median, 5). There were three intact copies of HMGA2 and one additional copy of the 5' part of the gene. These findings are consistent with previous reports that the ALT phenotype may be associated with a low or moderate level of gene amplification, whereas truncation of HMGA2 has been observed in both ALTs and benign lipomas. The aberrations in the present case were stable, although rare cells with higher MDM2 copy numbers were detected. Whether ALTs with these types of aberrations have a lower risk of tumor progression than ALTs with the notoriously mitotically unstable ring and giant marker chromosomes remains to be investigated.

Disruption and aberrant expression of HMGA2 as a consequence of diverse chromosomal translocations in myeloid malignancies

Chromosomal translocations that target HMGA2 at chromosome band 12q14 are seen in a variety of malignancies, notably lipoma, pleomorphic salivary adenoma and uterine leiomyoma. Although some HMGA2 fusion genes have been reported, several lines of evidence suggest that the critical pathogenic event is the expression of truncated HMGA2 isoforms. We report here the involvement of HMGA2 in six patients with myeloid neoplasia, dysplastic features and translocations or an inversion involving chromosome bands 12q13-15 and either 7p12, 8q22, 11q23, 12p11, 14q31 or 20q11. Breaks within or very close to HMGA2 were found in all six cases by molecular cytogenetic analysis, leading to overexpression of this gene as assessed by RT-PCR. Truncated transcripts consisting of HMGA2 exons 1-2 or exons 1-3 spliced to intron-derived sequences were identified in two patients, but were not seen in controls. These findings suggest that abnormalities of HMGA2 play an important and previously unsuspected role in myelodysplasia.

Constitutional rearrangement of the architectural factor HMGA2: a novel human phenotype including overgrowth and lipomas

Although somatic mutations in a number of genes have been associated with development of human tumors, such as lipomas, relatively few examples exist of germline mutations in these genes. Here we describe an 8-year-old boy who has a de novo pericentric inversion of chromosome 12, with breakpoints at p11.22 and q14.3, and a phenotype including extreme somatic overgrowth, advanced endochondral bone and dental ages, a cerebellar tumor, and multiple lipomas. His chromosomal inversion was found to truncate HMGA2, a gene that encodes an architectural factor involved in the etiology of many benign mesenchymal tumors and that maps to the 12q14.3 breakpoint. Similar truncations of murine Hmga2 in transgenic mice result in somatic overgrowth and, in particular, increased abundance of fat and lipomas, features strikingly similar to those observed in the child. This represents the first report of a constitutional rearrangement affecting HMGA2 and demonstrates the role of this gene in human growth and development. Systematic genetic analysis and clinical studies of this child may offer unique insights into the role of HMGA2 in adipogenesis, osteogenesis, and general growth control.

Genetic and expression profiles of cerebellar liponeurocytomas

Cerebellar liponeurocytoma, a rare, newly identified CNS neoplasm of adults, is characterized by advanced neuronal/neurocytic and focal lipomatous differentiation, low proliferative potential and a favorable clinical prognosis. Despite the different age distribution and benign biological behavior, the cerebellar liponeurocytoma shares several features with the cerebellar medulloblastoma, which may include an origin from the periventricular matrix of the fourth ventricle or the external granular layer of the cerebellum. To establish the genetic profile of cerebellar liponeurocytomas, we have formed an international consortium and collected tumor samples from 20 patients. DNA sequencing revealed TP53 missense mutations in 4 (20%) of 20 cerebellar liponeurocytomas, a frequency higher than in medulloblastomas. There was no case with PTCH, APC, or beta-catenin mutations, each of which may be present in subsets of medulloblastomas. Isochromosome 17q, a genetic hallmark of classic medulloblastomas, was not observed in any of the cases investigated by FISH analysis. cDNA array analyses were carried out on 4 cerebellar liponeurocytomas, 4 central neurocytomas, and 4 classic medulloblastomas. Cluster analysis of the cDNA expression data of 1176 genes grouped cerebellar liponeurocytomas close to central neurocytomas, but distinct from medulloblastomas. These results suggest cerebellar liponeurocytoma as a distinct tumor entity that is genetically different from medulloblastoma. Furthermore, the cDNA expression array data suggest a relationship to central neurocytomas, but the presence of TP53 mutations, which are absent in central neurocytomas, suggests that their genetic pathways are different.

Lipomatous hemangiopericytoma of the head and neck: immunohistochemical and DNA ploidy analyses

BACKGROUND

Lipomatous hemangiopericytoma (LHPC) is a newly described rare soft tissue tumor with unpredictable biologic behavior and is difficult to diagnose by conventional histologic parameters. The molecular analyses of this entity to date are sparse. Only a few cases of LHPC have been reported. Although one case of LHPC in the sinonasal region was briefly reported, this is the first case in the head and neck region with detailed clinicopathologic features and molecular analysis of this entity.

METHODS

We reported a case of LHPC in a 55-year-old woman with a slowly growing lesion in the occipital area that was diagnosed by CT and MRI and removed surgically. Immunohistochemical and DNA ploidy analyses were performed.

RESULTS

A panel of 16 markers was included for immunohistochemical analysis. Diffuse immunopositivity of CD57 in our case provides supportive evidence that LHPC is linked with HPC because this marker is also present in approximately 50% of conventional HPCs. CD57 should be used in the immunohistochemical panel in any lesion suspected to be LHPC. Furthermore, CD57 along with CD34 and XIIIa is thought to stain for primitive mesenchymal stem cells, suggesting a bimodal/multimodal differentiation of LHPC. By flow cytometry, we found that tumor cells were 100% diploid with the S-phase fraction (SPF) being 3.21%. A significant positive correlation was detected between nuclear proliferating index and SPF (p < 0.001, by Spearman analysis). These findings provide molecular evidence indicating a benign nature of LHPC.

CONCLUSIONS

Contrary to the old belief that HPC has an aggressive nature, this variant of tumor looks less aggressive. The patient was followed for 1 year without any evidence of recurrence, supporting our pathologic hypothesis.

Currarino syndrome: proposal of a diagnostic and therapeutic protocol

BACKGROUND/PURPOSE

The Currarino syndrome (CS) is a peculiar form of caudal regression syndrome (CRS) characterized by the association of hemisacrum, anorectal malformation (ARM), and presacral mass. The authors analyzed retrospectively their series, and they propose a multidisciplinary diagnostic and therapuetic protocol that until now has not been introduced.

METHODS

A series of 6 patients with CS is presented. Five of them were treated initially in other centers. None of them had an early diagnosis. All presented associated anomalies; in 50%, Hirschsprung's disease (HD) and other dysganglionoses were present. One patient died of a presacral ectopic nephroblastoma.

RESULTS

Depending on the expressivity, 3 types of CS can be identified, complete, mild, and minimal. Dysganglionoses and HD can be considered part of CS. A multidisciplinary diagnostic and therapeutic protocol is presented. Main points are sacrum x-Ray, molecular genetic diagnosis, radiologic evaluation of every member of CS families, magnetic resonance (MR) evaluation of patient spine and pelvis, suction rectal biopsies, and search for associated anomalies.

CONCLUSIONS

This protocol could give a valid contribution to the treatment of CS, allowing an early diagnosis and proposing a rational timing of multidisciplinary surgical procedures. Early diagnosis and treatment are essential to avoid morbidity and mortality from an undiagnosed presacral mass.

Retained heterodisomy for chromosome 12 in atypical lipomatous tumors: implications for ring chromosome formation

Atypical lipomatous tumor (ALT) is an intermediate malignant mesenchymal tumor that is characterized by supernumerary ring chromosomes and/or giant rod-shaped marker chromosomes (RGMC). Fluorescence in situ hybridization (FISH) and molecular genetic analyses have disclosed that the RGMCs always contain amplified sequences from the long arm of chromosome 12. Typically, RGMCs are the sole clonal changes and so far no deletions or other morphologic aberrations of the two normal-appearing chromosomes 12 that invariably are present have been detected. The mechanisms behind the formation of the RGMCs are unknown, but it could be hypothesized that RGMC formation is preceded by trisomy 12 or, alternatively, that ring formation of one chromosome 12 is followed by duplication of the remaining homolog. The latter scenario would always result in isodisomy for the two normal-appearing chromosomes 12, whereas the former would yield isodisomy in one-third of the cases. In order to investigate these possible mechanisms behind ring formation, we studied polymorphic loci on chromosome 12 in 14 cases of ALT showing one or more supernumerary ring chromosomes and few or no other clonal aberrations at cytogenetic analysis. The molecular genetic analyses showed that the tumor cells always retained both parental copies of chromosome 12, thus refuting the trisomy 12 and duplication hypotheses.

Intrascrotal Lipoblastoma With a Complex Karyotype: A Case Report and Review of the Literature

Lipoblastoma is a tumor of adipose tissue that usually occurs in young children. Most lipoblastomas occur on the extremities, trunk, and head and neck, and most have rearrangements of the 8q region. We describe a lipoblastoma in a 12-month-old boy who presented with a rapidly enlarging scrotal mass. Electron microscopy revealed features consistent with immature adipocytes, and cytogenetic analysis revealed the following karyotype: 57,XY,+4,+6,+7,der(8)t(8;12) (q22;q13), +der(8)t(8;12) (q22;q13), +9,+10,+12,−16,+17,+der(18)t(8;18)(q22;q23),+19,+20. Interestingly, the breakpoint on chromosome 12 (q13) is the same as that seen in lipoblastomas. To our knowledge, this is the first reported case of such a complex karyotype in lipoblastoma and adds to the expanding list of karyotypic abnormalities seen in such tumors.

Atypical lipomatous tumor: molecular characterization

PURPOSE OF REVIEW

Atypical lipomatous tumors/well-differentiated liposarcomas (ALT/WDLs) are one of the more frequent mesenchymal neoplasms and are characterized by specific chromosome aberrations: supernumerary chromosome or giant marker chromosome or both. Extra copies of known oncogenes such as MDM2, CDK4, SAS, HMGA2 and others are present in this abnormal genetic material.

RECENT FINDINGS

In the past few years, several papers have further dissected the genetic alterations present in these tumors, allowing the identification of new potential oncogenes.

SUMMARY

ALT/WDLs represent therefore an interesting model for assessing the potential role of these oncogenes, not only in the pathogenesis, but also as a therapeutic target.

Amplification of chromosome 1 sequences in lipomatous tumors and other sarcomas

Amplifications and gains involving 1q are common abnormalities in solid tumors. Recently, an amplicon originating from 1q21-23, containing the candidate oncogenes COAS1, COAS2 and COAS3 (Chromosome One Amplified Sequence) was identified. The presence, distribution and copy number level of extra COAS sequences were investigated in 48 bone and soft tissue tumor (BSTT) samples using metaphase FISH analysis. Amplification was seen in 27/48 (56%) samples. With few exceptions, all 3 genes were involved, but on average COAS2 exhibited higher copy numbers. The presence of extra COAS signals, irrespective of copy numbers, was found at similar frequencies in different histologic tumor subtypes. However, medium or high level amplification was common in lipomatous tumors but rare in other, nonlipomatous tumors (9/21 vs. 2/27 samples). The most common localization of extra COAS signals in lipomatous tumors was in supernumerary ring and giant marker chromosomes. Among nonlipomatous tumors, the distribution of extra COAS genes was more disperse, being located in various unidentified chromosomal structures, including double minutes, and only rarely in ring chromosomes. Because MDM2 is known to be amplified frequently in BSTTs, and in particular in atypical lipomatous tumors, cases with extra copies of COAS were studied also with an MDM2 probe. Twelve out of 18 lipomatous tumors had extra copies of both COAS and MDM2, and the 2 genes were found to be coamplified and interspersed exclusively in ring and giant marker chromosomes. Also 12 out of 18 nonlipomatous tumors exhibited simultaneous gain of COAS and MDM2, but colocalization in the same chromosome was less frequent. The role of the frequent coamplification of COAS, or some other yet unknown gene in the 1q21-23 region, and MDM2 remains to be elucidated.

Lipoma and opthalmoplegia in mitochondrial diabetes associated with small heteroplasmy level of 3243 tRNA(Leu(UUR)) mutation

We report a patient with mitochondrial diabetes mellitus associated with the A3243G mutation (MDM3243). The patient is a 77-year man with diabetes. At age 68, he noticed diplopia, due to superior rectus muscle palsy of the right eye. At age 70, he noticed lipoma on the right arm. The pathology of his muscle revealed some ragged-red fibers, and focal cytochrome c oxidase deficiency. Hence, he may have a pathogenetic mechanism in common with CPEO (chronic progressive external ophthalmoplegia) or mitochondria-related autoimmune disorder associated with mononeuropathy. He had the rate of 0.102% for heteroplasmy of 3243 mitochondrial DNA mutation in leukocytes. This case's heteroplasmy level is the smallest among the reported cases of MDM3243 in the literature. 3243 mitochondrial DNA mutation is known to induce a lack of uridine-modification in tRNA(Leu(UUR)) at the first letter of the anticodon, with which the third letter of the codon pairs, and decline of the pairing of the anticodon of tRNA with the codon of mRNA, suggesting the termination of polypeptide-elongation to generate premature proteins. Therefore, we speculate that these premature proteins may accumulate overtime, thereby affecting cells in target organs.

Distinct MDM2 and P14ARF expression and centrosome amplification in well-differentiated liposarcomas

Well-differentiated liposarcomas (WDLs) are common soft-tissue tumors in adults. They are characterized by large marker chromosomes and/or ring chromosomes containing 12q-derived sequences in which MDM2 is consistently amplified. WDLs are subdivided into two subtypes according to their karyotype. Type D cells exhibit a near-diploid karyotype, with very few or no chromosome changes. Type H cells exhibit a near-tetraploid karyotype and many structural changes. Expression of P14ARF, MDM2, and TP53 proteins was assayed in the two WDL subtypes to establish whether distinct expression profiles correlated with cell ploidy. Although a transcriptionally functional TP53 was present in most tumors independent of their karyotype, type H cells were characterized by high levels of P14ARF and MDM2 proteins. Although amplified within similar chromosome markers in type D tumors, MDM2 did not appear to be overexpressed. In addition, it was present as a C-terminal truncated protein, indicative of alternatively spliced variants of MDM2 mRNA. As the existence of karyotypically distinct tumors could result from alterations of the mitotic machinery, we investigated the centrosome behavior in the two WDL subtypes. Centrosome amplification occurred in WDL tumors types H and D independent of their ploidy status. Moreover, no functional centrosome difference was found between the two tumor subtypes.

New phenotype of accessory scrotum with perineal lipoblastoma: Coexistence of midperineal and lateral accessory scrotums

We present the extremely rare phenotype of an accessory scrotum with an associated lipoblastoma. There was a coexistence of midperineal and lateral types. To our knowledge, this phenotype has never been reported. The lipoblastoma, which arose in the perineum, divided the moving labioscrotal swelling into three parts during early fetal life. This resulted in the specific anomaly in this patient.

Evaluation ofMDM2 andCDK4 amplification by real-time PCR on paraffin wax-embedded material: a potential tool for the diagnosis of atypical lipomatous tumours/well-differentiated liposarcomas

Atypical lipomatous tumours/well-differentiated liposarcomas and dedifferentiated liposarcomas are characterized by 12q13-15 region amplification. In contrast, this molecular event has not been reported in benign lipomas. Within the 12q13-15 chromosomal region, the MDM2, SAS, HMGA2, and CDK4 genes are the most frequent targets of amplification. A series of lipomas (36 cases) and liposarcomas (48 cases) was analysed for MDM2 and CDK4 gene amplification by real-time PCR. MDM2 and CDK4 gene amplification was detected in 2.8% and 5.6% of lipomas and 98.2% and 82.4% of liposarcomas, respectively. Moreover, co-amplification of the two genes as well as a higher-level amplification was observed more frequently in dedifferentiated liposarcomas than in atypical lipomatous tumours/well-differentiated liposarcomas. Real-time PCR proved to be a fast and reliable method to characterize lipomas and liposarcomas by quantification of MDM2 and CDK4 gene amplification. It is applicable to paraffin wax-embedded tissues and could be useful when histological diagnosis is difficult.

Activating Gs α mutation at the arg201 codon in liposclerosing myxofibrous tumor

Liposclerosing myxofibrous tumor (LSMFT) is a benign fibro-osseous lesion that is characterized by mixture of histologic elements including lipoma, fibroxanthoma, myxoma, ischemic ossification, and fibrous dysplasia (FD)-like features. These tissue components are seen in the original reports of FD; however, the relationship between LSMFT and FD is not clear. Point mutation of the alpha subunit of G protein (Gs alpha), which increases cyclic adenosine monophosphate formation, has been recognized as the cause of McCune-Albright syndrome as well as polyostotic and monostotic FD of bone. Gs alpha mutation at the Arg201 codon in 2 patients of LSMFT was demonstrated in the present study. Although direct sequencing analysis using the fresh-frozen materials could not detect the mutation, the polymerase chain reaction fragmentation length polymorphism (PCR-RFLP) disclosed the missense point mutation Gs alpha at the Arg201 codon in 2 cases involving LSMFT. This result strongly suggests that a subset of LSMFT is a variant form of FD.

11q13 alterations in two cases of hibernoma: large heterozygous deletions and rearrangement breakpoints near GARP in 11q13.5

Hibernomas are rare, benign tumors with a histological appearance resembling that of brown adipose tissue. The diagnosis of hibernomas may be difficult because some of them contain only a small number of the characteristic multivacuolated fat cells and can be mistakenly classified as well-differentiated liposarcomas. Cytogenetic information has been reported for 10 cases, showing that these tumors are characterized by structural rearrangements involving 11q13. Previous fluorescence in situ hybridization (FISH) studies revealed consistent and sometimes cryptic losses of the MEN1 region in 11q13.1. Here, we describe the molecular cytogenetic analysis of two new hibernoma cases. Both tumors showed complex rearrangements, simultaneously including translocations, inversions, and deletions affecting the pair of chromosomes 11. The translocation partners were chromosome 5 in one case and chromosomes 16 and 22 in the other case. The 11q13 region was concomitantly rearranged on both chromosomes 11. FISH studies revealed large heterozygous deletions within the 11q13 band, from 11q13.1 to 11q13.5. Genes such as PYGM, MEN1, CCND1, FGF3, ARIX, and GARP were deleted, showing that the size of the 11q13 altered region was larger than previously reported. Furthermore, both tumors had breakpoints in 11q13.5, one of them in the immediate proximity of the GARP gene. Our results suggest that rearrangements of GARP or a neighboring gene may be important for the pathogenesis of hibernomas.

HMGA2 is expressed in an allele-specific manner in human lipomas

The architectural transcription factor HMGA2 is almost exclusively expressed in undifferentiated mesenchymal cells. Interestingly, it has been mapped to the translocation site in a variety of human mesenchymal tumors that reveal a terminally differentiated phenotype. The expression of chimeric HMGA2 transcripts encoding three DNA-binding domains fused to novel transcriptional regulatory domains was previously described in lipomas. In this study with lipoma ST91-198, we report the expression of truncated HMGA2 transcripts that gained no functional domains. The highly polymorphic region in the 5' untranslated region (UTR) of HMGA2 was used to determine the allele-specific expression of HMGA2 in lipomas. Microsatellite PCR revealed a monoallelic expression pattern, and only the translocated allele was expressed when the DNA-binding domains of the rearranged allele were fused with transcription activation domains. Surprisingly, a diallelic expression pattern of HMGA2 was observed in lipoma ST91-198, and the wild-type allele was also expressed. In conjunction with studies involving rearrangements of HMGA genes in other benign mesenchymal tumors, our results support a model in which the expression of the wild-type HMGA allele is critical for the pathogenesis of mesenchymal tumors and in which rearrangements of HMGA do not lead to a gain of function in the chimeric HMGA protein.

Lipoblastoma in a 23-year-old male: distinction from atypical lipomatous tumor using cytogenetic and fluorescence in-situ hybridization analysis

Lipoblastoma is a rare benign tumor that occurs primarily in infancy and early childhood. We present the rare presentation of a 12 cm sized intramuscular lipoblastoma of the thigh in a 23-year-old patient. On histology, the tumor strongly resembled an atypical lipomatous tumor due to the presence of lipoblasts and atypical stromal nuclei. The very focal lobulation and myxoid change presented the only histological hint towards a lipoblastoma. Cytogenetic and subsequent FISH evaluation of the tumor cells showed a 46,XY, t(8;15) (q12;q25) as chromosomal change with rearrangement of the PLAG1 gene. The present case indicates that lipoblastoma should enter the differential diagnosis of an 'atypical' deep seated fatty tumor in adults. The diagnostic value of cytogenetic/molecular analysis in the differential diagnosis of lipomatous tumors is underscored as well.

Infiltrating intramuscular lipoma of the temporal muscle. A case report with molecular cytogenetic analysis

Intramuscular lipomas are uncommon benign mesenchymal tumors which infiltrate skeletal muscle and are exceedingly rare in the head and neck region. Because of the infiltrating nature of the lesion and a high propensity for recurrence, they are sometimes difficult to distinguish from well-differentiated liposarcomas (WDLS). We report, the first case of an infiltrating lipoma of the temporal muscle in a 62-year-old white man who presented with a slow growing mass in the left temporal region. The histopathological examination showed diffuse infiltration of the striated muscle fibers by mature adipocytes. There were no lipoblasts or cells with atypical nuclei as described in WDLS. We performed interphase fluorescence in situ hybridization (FISH) analyses using painting probes for chromosome 12 and a specific probe for the MDM2 gene and comparative genomic hybridization. The results did not identify MDM2 or 12q amplification and therefore confirmed the benign nature of the lesion.

Clustering of deletions on chromosome 13 in benign and low-malignant lipomatous tumors

Deletions and structural rearrangements of the long arm of chromosome 13 are frequently observed in benign and low-malignant lipomatous tumors, but nothing is known about their molecular genetic consequences. We assessed the karyotypes of 40 new and 22 previously published cases (35 ordinary lipomas, 15 spindle cell/pleomorphic lipomas, 2 myxolipomas, 1 angiomyxolipoma and 9 atypical lipomatous tumors) with chromosome 13-abnormalities, and found bands 13q12-22 to be frequently affected. Twenty-seven cases with structural abnormalities within this region were selected for breakpoint and deletion mapping by metaphase fluorescence in situ hybridization (FISH), using a set of 20 probes. Deletions were found in 23 of 27 cases. The remaining 4 cases had seemingly balanced rearrangements. The breakpoints were scattered but clustered to band 13q14, and in all cases with unbalanced abnormalities, a limited region within band 13q14 was partially or completely deleted. A deletion within band 13q14 was found together with a breakpoint on the other homologue in 5 cases, 4 of which could be tested further with regard to the status of the retinoblastoma (RB1)-gene. In all 4 cases, only 1 copy of the gene was deleted. In addition to the breaks and deletions in the vicinity of the RB1-locus, several other regions of 13q were recurrently affected, e.g., in the vicinity of the hereditary breast cancer (BRCA2; 13q12)- and lipoma HMGIC fusion partner (LHFP; 13q13)- genes. Our findings strongly indicate that deletion of a limited region (approximately 2.5 Mbp) within 13q14, distal to the RB1-locus, is of importance in the development of a subset of lipomatous tumors.

Characterization of supernumerary rings and giant marker chromosomes in well-differentiated lipomatous tumors by a combination of G-banding, CGH, M-FISH, and chromosome- and locus-specific FISH

Supernumerary ring chromosomes and/or giant marker chromosomes are often seen in soft-tissue tumors of low-grade or borderline malignancy, such as well-differentiated liposarcomas or atypical lipomas. Classic cytogenetic banding techniques have proved insufficient to identify the genomic composition and structure of such rings and markers, but fluorescent in situ hybridization (FISH) studies have shown that they consist mainly of amplified material from chromosome 12, more specifically from bands 12q13-->q15. We have used the new FISH-based screening techniques comparative genomic hybridization (CGH) and multicolor-FISH (M-FISH) in combination with G-banding and analysis by chromosome- and locus-specific fluorescent in situ probes to examine in detail the karyotypic characteristics of 22 lipomatous tumors, most of them classified histologically as well-differentiated liposarcomas, selected because they had been shown to harbor rings and/or marker chromosomes. M-FISH, in contrast to G- banding, was found to be informative with regard to the chromosomal origin of the rings and other markers present, whereas CGH and hybridizations with locus-specific probes helped identify which subchromosomal regions were involved. We found that chromosome bands 12q15-->q21 were always gained, with 12q15-->q21 being amplified (i.e., a green-to-red ratio >2 by CGH) in 14 of 22 tumors. In three tumors, two distinct but close amplicons in 12q could be identified, corresponding to bands 12q13-->q15 and 12q21. The genomic segment 1q21-->q23 was gained in 12 cases, reaching the level of amplification in seven. Bands 6q24 and 7p15, whose pathogenetic involvement in liposarcomas has not been reported previously, were gained in three cases each. In addition, the rings and giant markers often contained interspersed sequences from several other chromosomes that did not give an equally clear impression of being nonrandomly involved.

Atypical lipomatous tumor in a 14-year-old patient: distinction from lipoblastoma using FISH analysis

Liposarcomas are rare in young age. We present the rare case of an atypical lipomatous tumor (synonym: well-differentiated lipoma-like liposarcoma) in a 14-year-old girl with the differential diagnosis of lipoblastoma which was excluded by fluorescence in situ hybridization (FISH) analysis. The tumor presented as a soft tissue mass at the dorsal part of the right thigh measuring up to 18 cm. Microscopically the lesion consisted of atypical adipocytes with hyperchromatic nuclei and additional multivacuolated lipoblasts. Interphase dual-color FISH performed with chromosome 8 centromeric and YAC164H5 (mapping to exons 2-5 of the PLAG1 gene) probes revealed no rearrangement of PLAG1 oncogene or polysomy of chromosome 8. Additional FISH using an MDM2 gene probe and an BAC534N15 probe (containing sequences specific for the CDK4 gene) showed amplification of the CDK4 gene. These findings indicate that this tumor was no lipoblastoma but an atypical lipomatous tumor, which is of clinical relevance. In young individuals the distinction between lipoblastoma and liposarcoma is often impossible by light microscopy alone. This case shows that FISH can serve as a decisive tool in the differential diagnosis of lipoblastoma and lipoma-like liposarcoma apart from its role in distinction between lipoblastoma and myxoid/round cell liposarcoma.

Fusion of RDC1 with HMGA2 in lipomas as the result of chromosome aberrations involving 2q35-37 and 12q13-15

Rearrangements of chromosome bands 12q13-15 are frequent in various benign mesenchymal and epithelial tumors, and the gene HMGA2 seems to be the most common target within this chromosome region. In the majority of cases, the rearrangements result in a fusion of the first three exons of HMGA2 with different translocation partners. Despite the large number of HMGA2 mutations that have been reported, very little is known about the fusion partners. In this study, we have characterized a recurrent fusion of the first three exons of HMGA2 5' to the G protein-coupled receptor gene (RDC1) in lipomas with rearrangements involving chromosome bands 2q35-37 and 12q13-15, one of several recurrent chromosomal rearrangements in lipomas. The functional impact of the fusion is truncation of HMGA2, because the RDC1 part contributes with a stop codon one amino acid downstream of the breakpoint. The breakpoint within RDC1 was localized in a previously uncharacterized exon of the gene, and our data suggest that RDC1 is subject to alternative splicing.

A novel LPP fusion gene indicates the crucial role of truncated LPP proteins in lipomas and pulmonary chondroid hamartomas

The lipoma preferred partner (LPP) gene is fused to the high mobility group protein gene HMGIC in lipomas and pulmonary chondroid hamartomas. In addition, a fusion of LPP to the mixed lineage leukemia (MLL) gene has been described in a case of acute myeloid leukemia. Herein, a novel LPP fusion transcript of LPP in a lipoma is described that points to the possible oncogenic potential of LPP.

[From cytogenetics to cytogenomics of adipose tissue tumors: 1. Benign adipose tissue tumors]

Benign lipomatous tumors are characterized at the genetic level by different types of chromosomal abnormalities. A rearrangement of the HMGIC (HMGA2) gene, localized in 12q15 and coding for an architectural non-histone DNA protein, is observed in a majority of solitary superficial lipomas. Alterations of HMGIC are often resulting from reciprocal translocations, such as t(3;12)(q27-28;q15) that fuses LPP with HMGIC, but a variety of chromosomal anomalies, such as deletions, inversions or insertions are also observed. Rearrangements of chromosomal regions 6p21-22, 13q, 11q13, 12q13 or others are described in approximately one third of superficial lipoma cases with abnormal karyotypes. The genes involved in these alterations remain to be determined. Lipoblastomas are pediatric neoplasms that are characterized by rearrangements of PLAG1, located in 8q11-12 whereas hibernomas, that resemble brown fat, are associated with 11q13 rearrangements together with often complex chromosomal alterations. Deletions of 13q and 16q have been identified in spindle cell lipomas. A t(11;16)(q13;p12-13) have been described in the two published karyotypes of chondroid lipomas. The chromosomal features of other rare benign lipomatous tumors, the differential diagnosis of which is occasionally difficult, such as infiltrating intra-muscular lipomas, organic deep-seated lipomas, or angiomyolipomas, myolipomas, myxolipomas are still poorly defined. Although the genetic characterization of benign lipomatous tumors has been dramatically in progress over the last ten years, many aspects remain obscure and warrant future investigations for a better comprehension of underlying molecular mechanisms.

Multiple pericallosal lipomas in two siblings with frontonasal dysplasia

We report cases of two siblings with frontonasal dysplasia (FND) associated with multiple pericallosal lipomas in almost similar locations. In each sibling two separate curvilinear pericallosal lipomas were present-one in relation to the posterior part of the corpus callosum and the other in relation to the rostrum. To our knowledge, multiple pericallosal lipomas in association with FND have not been described before. Pericallosal lipomas in cases of FND are of the tubulonodular type; they have been reported only in relation to the anterior part of the corpus callosum.

Rearrangement involving chromosomes 1 and 8 in a retroperitoneal lipoma

Superficial lipomas are very common benign adipose tissue tumors. In contrast, deep-seated lipomas such as retroperitoneal lipomas, are extremely rare and have to be carefully distinguished from well-differentiated liposarcomas for appropriate treatment and follow-up. We report to, our knowledge, the first cytogenetic analysis of a retroperitoneal lipoma occurring in an adult, which showed a complex rearrangement interpreted as t(1;8)(q32;q22-q23) followed by a pericentric inversion of der(8). There was no detectable rearrangement of chromosome 12, and in particular no 12q14-q15 amplification. Because rearrangements of the 8q11-q13 region involving the PLAG1 gene have been described in lipoblastoma-another kind of benign adipose tumor--we used fluorescence in situ hybridization analysis to determine in the present case the chromosomal breakpoint on 8q was located between the ETO (8q22) and COX6C (8q22-q23) genes at a great distance from PLAG1. Karyotypic analysis of additional cases of retroperitoneal lipomas will be required to assess the significance of chromosome 1 and 8 rearrangements in a continuous effort to attain a better classification of adipose tissue tumors. Of great importance is the determination of such genetic markers as additional tools for the differential diagnosis between benign and malignant forms of adipose tumors, and to avoid erroneous diagnoses.

Distinction between lipoma and liposarcoma by MDM2 alterations: a case report of simultaneously occurring tumors and review of the literature

We investigated a lipoma and a well-differentiated/dedifferentiated liposarcoma (WD/DDL), occurring simultaneously in one patient for the possible role of p53 and mdm2 in the molecular oncogenesis of liposarcoma and tumor progression. The hypothesis tested was if there is a continuum in the development from lipoma to liposarcoma. Lipoma was characterized by a lack of p53 mutation, p53 LOH and p53 protein expression, as well as by mdm2 amplification and mdm2 protein expression. p53 mutation and p53 LOH were found neither in the well-differentiated nor in the dedifferentiated parts of the liposarcoma. In contrast, mdm2 amplification and an increase in mdm2 protein expression were found to be associated with malignancy and dedifferentiation, whereas p53 protein expression was only slightly increased. These findings indicate that mdm2 constitutes one of the most common targets for molecular aberration in WD/DDL. We suggest that mdm2 is a marker distinguishing between ordinary lipoma and well-differentiated liposarcoma, and that the genesis of these tumors is different.