Lipoblastoma in adolescents and young adults: report of six cases with FISH analysis

Head and neck lipoblastoma in children: A case report and systematic review

BACKGROUND

Lipoblastoma is a rare and benign tumor arising from embryonal fat cells. It develops primarily in infancy and early childhood. We present a case study of a 10-month-old child treated for an extensive tumor of the infratemporal fossa and parapharyngeal space. The systematic review of 60 reports in 80 children with lipoblastoma of the head and neck is also reported.

MATERIAL AND METHODS

Systematic review of all articles included lipoblastomas of the head and neck area in children published from 1964 to 2022 in the PubMed database was conducted. Clinical presentation of extensive lipoblastoma of the head and neck in a child.

RESULTS

On the basis of all inclusion criteria 83 articles were identified concerning pediatric lipoblastoma. There were 36 F (45%) and 39 M (48%), in 6 patients, (7%) gender was not specified. Ages ranged from 0mth (6h) to 15 yo (180mth). The tumor was located in the head in 22 (27%) cases, while the neck area accounted for 53 (65%) cases. General description without precise location was shown in 6 (7%) cases. All patients underwent complete surgical excision. Post surgical recurrence was noted in 6% clinical cases in the analyzed articles.

CONCLUSIONS

Lipoblastoma is characterized by a rapidly growing predominantly adipose mass. The treatment of choice is complete surgical excision. In selected cases when the pathology is hard to reach, as a consequence of the extensive penetration of the mass, we recommend performing the procedure with an interdisciplinary team. Endoscopy assistance and microdebrider significantly facilitated the removal of pathology in the described advanced case of lipoblastoma. This is the only case reported in the pediatric literature of a head and neck lipoblastoma, where due to extensive involvement and location of the disease the cranial nerves V2 and inferior alveolar branch of V3 could not be spared. Long-term follow-up even to 10 years is required because there is a reported tendency for these tumors to recur.

Lipoblastoma Arising in the Head and Neck: A Clinicopathologic Analysis of 20 Cases

BACKGROUND

Lipoblastomas (LPBs) are benign adipocytic neoplasms believed to recapitulate the development of embryonal fat.

METHODS

We investigated the clinicopathologic and immunohistochemical features of 20 lipoblastomas arising in the head and neck in 18 patients.

RESULTS

Patients included 6 males and 12 females (1:2 ratio) with age at diagnosis ranging from 4 months to 28 years. Tumors occurred more commonly in the neck (12, 66.7%) and less commonly in the forehead, scalp, and tongue (2, 11.1%). Tumor size ranged from 1.4 to 6.0 cm (median 5.0 cm). Two patients, a 4-month-old female and 3-year-old male, had local recurrence of neck tumors at 4 months and 3 years after excision, respectively. Microscopically, tumors had a lobulated growth pattern and consisted of adipocytes at varying stages of differentiation. In addition to the classical histologic features, lipoma-like and myxoid variants constituted 45% of cases. Metaplastic elements, including brown fat and cartilage, were identified in two cases.

CONCLUSIONS

LPBs arising in the head and neck region are not uncommon and occurred at a rate of 9% in our cohort. They should be kept in the differential diagnosis when a fatty tumor is encountered in an older child or occurring at an unusual location.

Lipoblastoma in one adult and 35 pediatric patients: Retrospective analysis of 36 cases

Lipoblastoma is a rare benign mesenchymal neoplasm that typically occurs at various sites in infants and children but may also occur in adults. Thus, differential diagnoses are often performed. To understand this tumor type, the present study described clinicopathological features, diagnosis and differential diagnosis of different morphological lipoblastomas. A single-institution retrospective review of 36 lipoblastoma cases diagnosed between 2015 and 2021 was performed. Formalin-fixed paraffin-embedded tissue was used for S-100, CD34, P16 and desmin immunohistochemistry analysis, along with rapid fluorescence in situ hybridization (FISH) detection with pleiomorphic adenoma gene 1 (PLAG1). The 36 cases included 14 females and 22 males [age range, 7 days to 33 years (median, 16.5 years); 28 patients were aged ≤3 years] and the tumors were located in the trunk (n=16), limbs (n=12), head and neck (n=6), and perineum (n=2). Histologically, lipoblastomas were divided into classic (n=15), lipoma-like (n=13) and myxoid (n=8) subtypes. They comprised lobules of mature adipose tissue of varying size and a fine capillary network surrounded by mucinous stroma. Single- or multivesicular lipoblasts positive for S-100 (29/36, 81%) were observed, with occasional mature adipocytes. Peripheral vessels and cytoplasm of primitive mesenchymal cells were diffusely positive for CD34 (36/36, 100%), whereas primitive mesenchymal cells and striated muscle tissue were positive for desmin (26/36, 72%). Most tumor cells were negative while only few were positive for P16 (8/36, 22%). FISH revealed PLAG1 breakage and rearrangement in 24/32 (75%) patients. In total, 28 patients were followed up post-operatively (range, 2-84 months; median, 41 months; 3 patients relapsed and 8 were lost to follow-up). In conclusion, diagnosis of a typical lipoblastoma is not difficult and PLAG1 breakage detection is key for the diagnosis.

Update of Pediatric Lipomatous Lesions: A Clinicopathological, Immunohistochemical and Molecular Overview

Lipomatous neoplasms are a rare entity in the pediatric population, comprising less than 10% of soft tissue tumors in the first two decades of life. Some characteristics of pediatric adipocytic tumors are analogous to their adult counterparts, some pediatric lipomatous lesions however harbor unique features. In recent years, there have been significant advances in the understanding of the pathogenesis and hence in the classification and treatment of pediatric adipocytic tumors. This literature-based article will provide a review of the presently known clinicopathological, immunohistochemical and molecular features of pediatric lipomatous lesions.

The histological and molecular spectrum of lipoblastoma: A case series with identification of three novel gene fusions by targeted RNA-sequencing

Lipoblastoma is a rare benign mesenchymal neoplasm that typically occurs in infancy but may also occur in older age groups and various locations. Thus, there are often numerous clinical differential diagnoses. Moreover, lipoblastomas can show a broad histologic spectrum, which can hamper the correct diagnosis, particularly in small biopsies. At the genomic level, lipoblastomas are characterized by chromosomal fusions involving the PLAG1 gene. We investigated 11 lipoblastoma samples from 10 pediatric patients (age range five months to 12 years), including one patient with local recurrence, in view of their histopathological features, and performed targeted RNA sequencing. We found a broad histological spectrum with some tumors with prominent myxoid changes, but also tumors composed mainly of mature adipocytic cells, and classified the cases according to the literature as classic (mixed), maturing, or myxoid subtype. By targeted RNA sequencing analysis, we identified characteristic PLAG1 rearrangements in 70% of the investigated cases. Moreover, these analyses revealed three novel gene fusions, two affecting the PLAG1 gene and one involving HMGA2. Besides, we performed PLAG1 immunohistochemistry and identified positive cells, typically immature adipocytic cells and spindle cells, at various numbers in all cases. However, in the maturing areas, only very sparsely positive cells were found, limiting the value of the PLAG1 immunohistochemistry as an adjunct in the diagnosis of lipoblastoma, particularly for the maturing subtype and small biopsies. The presented case series confirms the broad morphological spectrum of lipoblastoma described in the literature and underlines the value of modern molecular diagnostic approaches as a supportive diagnostic tool in challenging cases and for gaining further insights into the molecular basis of this rare mesenchymal tumor.

Head and neck lipoblastomas: Report of 3 cases and review of the literature

INTRODUCTION

Lipoblastoma is a rare benign tumor arising from embryonic white fat which occurs in the early childhood. It usually arises on the extremities and considered as a rare cause of a pediatric head and neck masses. The aim of this study is to shed light on lipoblastomas as a differential diagnosis of rapidly growing soft fatty masses of children in neck and head area.

PATIENTS AND METHODS

A retrospective review of 3 patients with lipoblastoma, underwent Surgical resection (case 1 and 2) by cervical approach. The third patient with a facial lipoblastoma was not operated due to the high risk of facial paralysis. Review of literature, diagnostic methods and genetics of lipomatous tumors are discussed.

RESULTS

Complete surgical excision via a cervical approach demonstrated irregular lobules of immature fat cells separated by a loose, myxoid connective tissue. Histology analysis confirmed the diagnosis of lipoblastoma.

DISCUSSION

Lipoblastoma is a rare childhood tumor, even rarer in head and neck area. The pathogenesis is unknown, though it is believed to arise from altered embryogenesis of human white fat and genetic predisposition, as chromosome 8 abnormalities may be implicated in the development of lipoblastoma. The presumptive diagnosis is performed by imaging. The most important differential diagnosis of lipoblastoma is myxoid liposarcoma. The mainstay of treatment is complete non-mutilating resection of the tumor to avoid recurrence.

CONCLUSION

Lipoblastoma should be suspected in case of heterogeneous fatty tumor in head and neck area, and included as a differential diagnosis of cervical masses in children younger than 3 years. The mainstay of treatment is complete surgical excision with a good prognosis.

A large retroperitoneal lipoblastoma as an incidental finding: a case report

Background

Lipoblastoma is a rare benign mesenchymal neoplasm of infancy that most commonly occurs on the extremities and trunk but can arise at variable sites of the body. Retroperitoneal lipoblastomas are particularly rare but can grow to enormous size, and preoperative diagnosis is difficult with diverse, mostly malignant differential diagnoses that would lead to aggressive therapy. Since lipoblastoma is a benign tumor that has an excellent prognosis after resection, correct diagnosis is crucial.

Case presentation

A case of a large retroperitoneal tumor of a 24-month old infant that was clinically suspicious of a malignant tumor is presented. Due to proximity to the right kidney, clinically most probably a nephroblastoma or clear cell sarcoma of the kidney was suspected. Radiological findings were ambiguous. Therefore, the mass was biopsied, and histology revealed an adipocytic lesion. Although mostly composed of mature adipocytes, in view of the age of the patient, the differential diagnosis of a (maturing) lipoblastoma was raised, which was supported by molecular analysis demonstrating a HAS2-PLAG1 fusion. The tumor was completely resected, and further histopathological workup led to the final diagnosis of a 13 cm large retroperitoneal maturing lipoblastoma. The child recovered promptly from surgery and showed no evidence of recurrence so far.

Conclusion

Although rare, lipoblastoma should be included in the differential diagnoses of retroperitoneal tumors in infants and children, and molecular diagnostic approaches could be a helpful diagnostic adjunct in challenging cases.

Lipoblastomas presenting in older children and adults: analysis of 22 cases with identification of novel PLAG1 fusion partners

Lipoblastomas are benign neoplasms of embryonal white fat that typically present in the first 3 years of life and show a lobular arrangement of maturing adipocytes with variable degrees of myxoid change. We systematically studied the clinicopathologic and genetic features of lipoblastomas arising in older children and adults. Cases with a diagnosis of lipoblastoma or maturing lipoblastoma in patients >3 years of age were retrieved from our archives. Immunostaining for CD34 and desmin and molecular studies (FISH, RNA sequencing) were performed. Twenty-two cases (8F; 14M) were identified in patients ranging from 4 to 44 years of age (median 10 years). Sites included extremity (n = 15), head and neck (n = 4), and trunk (n = 3) with tumor sizes varying from 1.6 to 17.5 cm (median 5). Only three tumors had histologic features of "conventional" lipoblastoma. The majority of tumors (n = 14) were composed of variably sized lobules of mature adipose tissue partitioned by thin fibrous septa ("maturing"). The remaining five cases consisted predominantly of bland spindled to plump ovoid cells embedded in a fibrous stroma, with a vaguely plexiform arrangement of small myxoid and adipocytic nodules ("fibroblastic"). CD34 was diffusely positive in all cases tested (21/21), while desmin immunoreactivity was identified in 12 of 21 cases (diffuse = 7, focal = 5). PLAG1 rearrangements were identified in 13 tumors in the entire cohort (59%), including all 5 fibroblastic tumors. RNA sequencing detected eight PLAG1 fusion partners, of which two were known (CHCHD7 and COL3A1) and six were novel (SRSF3, HNRNPC, PCMTD1, YWHAZ, CTDSP2, and PPP2R2A). Twelve cases had follow-up (1-107 months; median 21 months), and no recurrences were reported. Lipoblastomas may occur in older children and adults and may be difficult to recognize due to their predominantly adipocytic or fibrous appearance. Awareness that lipoblastomas may occur in older patients, careful evaluation for foci showing more typical morphologic features, ancillary immunohistochemistry for CD34 and desmin, and molecular genetic studies to identify PLAG1 rearrangements are the keys to recognizing these tumors.

Follow-up outcomes of pediatric patients who underwent surgical resection for lipoblastomas or lipoblastomatosis: a single-institution experience with a systematic review and meta-analysis

PURPOSE

The objective of this study was to examine the long-term outcomes of pediatric patients who underwent surgical resection for lipoblastoma and lipoblastomatosis (LB/LBM).

METHODS

A single-center retrospective study of pediatric patients with LB/LBMs seen between 1991 and 2015 was conducted. A systematic review, including studies published prior to late August 2018, was performed. Using a random effect meta-analysis, pooled weighted proportions and unadjusted odds ratios (OR) with 95% confidence intervals (CI) were calculated.

RESULTS

The retrospective study included 16 patients, while the systematic review included 19 published studies consisting of 381 patients. Among 329 (82%) patients with follow-up information, the pooled recurrence rate was 16.8% (95% CI 10.9-23.5%; I² = 59%). The reported time to recurrence ranged from < 1 to 8 years. Recurrence risk was greater for incomplete (n = 34) than complete resection (n = 150): OR 11.4 (95% CI 3.0-43.6; I² = 43%). LBMs (n = 35) had a greater recurrence risk than LBs (n = 116): OR 5.5 (95% CI 1.9-15.9; I² = 0%). Recurrences were higher for studies with approximately ≥ 3 years of follow-up versus studies with < 3 years of follow-up.

CONCLUSION

Recurrences are more likely to occur with LBMs and/or incomplete resection. Follow-up beyond 3-5 years should be considered given that the recurrence risk appears to be greater in the long-term.

Intrascrotal lipoblastoma in adulthood

This case report describes the case of a 37-year-old man that noticed an intrascrotal right mass with 1 month of evolution. During physical exam presented with a large mass at the inferior portion of the right testicle, clearly separated from the testicle, with a tender consistency and mobile. An ultrasound was performed that showed a solid and subcutaneous nodular lesion, extra testicular, heterogeneous, measuring 7.2 cm. Pelvic magnetic resonance imageMRI showed a lesion compatible with a lipoma. The patient was subjected to surgical excision of the lesion by scrotal access, having histology revealed a lipoblastoma (LB) of the scrotum. Histological diagnosis was obtained by microscopic characteristics (well-circumscribed fatty neoplasm) and immunohistochemistry (stains for CD34, S100 protein and PLAG1 were positive; stains for MDM2 and CDK4 were negative). LB is extremely rare after adolescence in any location, being this first described case of intrascrotal LB described in adulthood.

A contemporary review of myxoid adipocytic tumors

Myxoid adipocytic tumors encompass a broad heterogeneous group of benign and malignant adipocytic tumors, which are typically myxoid (e.g. myxoid liposarcoma, lipoblastoma and lipoblastoma-like tumor of the vulva) or may occasionally appear predominantly myxoid (e.g. pleomorphic liposarcoma, atypical lipomatous tumor, dedifferentiated liposarcoma, chondroid lipoma, spindle cell/pleomorphic lipoma, atypical spindle cell lipomatous tumor and atypical pleomorphic lipomatous tumor). There have been significant advances in recent years in classification and understanding the pathogenesis of adipocytic tumors, based on the correlation of histologic, immunohistochemical, and cytogenetic/molecular findings. Despite these advances, the morphologic diagnosis and accurate classification of a myxoid adipocytic tumor can be challenging due to major morphologic overlap between myxoid adipocytic and non-adipocytic tumors. This article will provide a review on the currently known morphological, immunohistochemical and molecular features of myxoid adipocytic tumors and their differential diagnosis.

Undifferentiated myxoid lipoblastoma with PLAG1-HAS2 fusion in an infant; morphologically mimicking primitive myxoid mesenchymal tumor of infancy (PMMTI)--diagnostic importance of cytogenetic and molecular testing and literature review

Lipoblastoma is a benign myxoid neoplasm arising in young children that typically demonstrates adipose differentiation. It is often morphologically indistinguishable from primitive myxoid mesenchymal tumor of infancy (PMMTI), which is characterized by a well-circumscribed myxoid mass with a proliferation of primitive mesenchymal cells with mild cytologic atypia. PMMTI occurs in the first year of life and is known to have locally aggressive behavior. No specific genetic rearrangements have been reported to date. In contrast, the presence of PLAG1 (Pleomorphic Adenoma Gene 1) rearrangement is diagnostic for lipoblastoma. We hereby demonstrate the combined application of multiple approaches to tackle the diagnostic challenges of a rapidly growing neck tumor in a 3-month-old female. An incisional tumor biopsy had features of an undifferentiated, myxoid mesenchymal neoplasm mimicking PMMTI. However, tumor cells showed diffuse nuclear expression by immunohistochemical (IHC) stain. Conventional cytogenetic and fluorescence in situ hybridization (FISH) analyses as well as next generation sequencing (NGS) demonstrated evidence of PLAG1 rearrangement, confirming the diagnosis of lipoblastoma. This experience warrants that undifferentiated myxoid lipoblastoma can mimic PMMTI, and the combination of cytogenetic and molecular approaches is essential to distinguish these two myxoid neoplasms. Literature on lipoblastomas with relevant molecular and cytogenetic findings is summarized. Our case is the first lipoblastoma diagnosed with a PLAG1 fusion defined by NGS technology.

Immunohistochemical expression of p16 in lipoblastomas

Lipoblastoma (LB) is a rare benign adipocytic tumor of childhood occasionally showing histological similarities to myxoid liposarcoma (ML) or well-differentiated liposarcoma (WDL). p16 immunohistochemistry has proved to be useful in distinguishing various types of liposarcomas, in particular WDL from lipoma, with higher sensitivity and specificity than MDM2 and CDK4 immunohistochemistry. In this study, we reported the histologic features of a series of 30 LB with emphasis on the potential diagnostic pitfalls and investigated the immunohistochemical expression of p16. Moreover, p16 immunostaining was performed in 16 liposarcomas (11 WDL and 5 ML), 16 lipomas, and 16 cases of liponecrosis in order to evaluate its usefulness in the differential diagnosis of challenging lesions occurring in older children. Overall, p16 immunostaining was positive in 3 LBs and in 12 out of 16 liposarcomas (10 WDL and 2 ML), with a sensitivity of 75%, a specificity of 90%, a positive predictive value of 80%, and a negative predictive value of 87%. All lipomas were p16 negative, whereas 5 liponecroses were positive. Accounting altogether the benign lesions versus liposarcomas, p16 showed a sensitivity of 75%, a specificity of 87%, a positive predictive value of 60%, and a negative predictive value of 93%. Our data suggest that a negative p16 immunostaining may be helpful in excluding a liposarcoma when occurring in unusual clinical contexts, such as in adolescence or late recurrence. However, such finding should be interpreted with caution since also some liposarcomas lack p16 and occasional LBs are positive.

A case of unusual histology of infantile lipoblastoma confirmed by PLAG1 rearrangement

Lipoblastoma, a relatively rare benign adipose neoplasm, predominantly affects children younger than 3 years of age. We herein report the case of a 7-month-old girl with an unusual myxomatous histology of lipoblastoma. A rapidly growing mass was detected in the subcutaneous area of the left buttock. Histologically, the tumor consisted of abundant myxoid stroma exhibiting cellular atypia and a high mitotic activity. Although the histological findings were unusual, the tumor was diagnosed as a lipoblastoma according to both PLAG1 immunohistochemistry and the presence of PLAG1 rearrangement on fluorescence in situ hybridization.

Identification of COL3A1 and RAB2A as novel translocation partner genes of PLAG1 in lipoblastoma

Lipoblastoma is a rapidly growing, benign neoplasm in children. Surgical excision is usually curative, with a recurrence rate of about 20%. Because the histology of lipoblastoma is heterogeneous and overlaps with other lipomatous tumors, some lipoblastoma cases have been difficult to diagnose. The detection of PLAG1 gene rearrangement is useful for the diagnosis of lipoblastoma. Three fusion partner genes are known in relation to PLAG1 in lipoblastoma HAS2 at 8q24.1, COL1A2 at 7q22, and RAD51L1 at 14q24. Herein, we describe another two novel fusion genes in lipoblastoma tumor specimens. We checked six tumors for the presence of two known fusion genes, HAS2-PLAG1 and COL1A2-PLAG1. Only HAS2-PLAG1 was found in one of the cases. Next, we attempted to identify potential PLAG1 fusion partners using 5'RACE. Sequence analysis revealed two novel fusion genes, COL3A1-PLAG1 in three cases and RAB2A-PLAG1 in one case, respectively. As a result of the translocations, the constitutively active promoter of the partner gene drives the ectopic expression of PLAG1. We also evaluated whether a high level of PLAG1 expression can be used to help differentiate lipomatous tumors. PLAG1 expression was evaluated by real-time PCR in five lipoblastoma tumor specimens. The expressions were 70-150 times higher in lipoblastomas than in human adipocytes. However, PLAG1 expression was low in one case of lipoma. These results demonstrate that PLAG1 overexpression is a potential marker of lipoblastoma. Our findings, in agreement with previous studies, show that lipoblastoma is a group of lipomatous tumors with PLAG1 rearrangement and overexpression. © 2014 Wiley Periodicals, Inc.

A novel PLAG1-RAD51L1 gene fusion resulting from a t(8;14)(q12;q24) in a case of lipoblastoma

Lipoblastomas are rare benign tumors that arise from embryonic adipose tissue and occur predominantly in the pediatric population. Here, we report a case of lipoblastoma in an 8-month-old boy. Surgical excision and subsequent histopathologic examination were consistent with features of lipoblastoma. Chromosome analysis of the tumor revealed a clonal unbalanced t(8;14) translocation. Genomic microarray analysis of the tumor delineated the exact breakpoints at 8q12.1 and 14q24.1, which involved the PLAG1 and RADA51L1 genes, respectively. Furthermore, fluorescence in situ hybridization demonstrated that the translocation fused the PLAG1-RAD51L1 genes. These results suggest that RAD51L1 is an alternative fusion partner gene for the PLAG1 gene in a lipoblastoma with an 8q12 rearrangement.

Cytogenetic analysis in the diagnosis and management of lipoblastomas: results from a single institution

BACKGROUND

Lipoblastomas are rare, benign, soft tissue tumors that occur primarily in young children. Treatment includes complete excision and surveillance for recurrence. Lipoblastomas can be indistinguishable from other benign lipomatous tumors and liposarcomas. Cytogenetic analysis can provide the definitive diagnosis in questionable cases, because benign and malignant lipomatous tumors exhibit specific nonrandom cytogenetic abnormalities. The purpose of the present study was to discuss the disease management and outcomes in a large contemporary group of patients with lipoblastoma.

MATERIALS AND METHODS

A retrospective chart review of patients diagnosed with lipoblastoma presenting from 2000-2011 was conducted. The data from these patients were compared with data from a previously published historical group of patients (1985-1999) from the same children's hospital.

RESULTS

We identified 37 patients in the contemporary cohort group and compared them with 25 patients from the historical group. The tumor involvement sites were similar. The current cohort group had a lower recurrence rate, although this might have been underestimated owing to a shorter follow-up period (median 1.4 y, range 2 wk to 11.0 y). Preoperative imaging findings led to an incorrect diagnosis in 62% of the patients. Cytogenetic analysis was used to help determine the final diagnosis in 50% of the cases. In 39% of cases, translocations involved the long arm of chromosome 8, the most common anomaly in lipoblastoma.

CONCLUSIONS

Lipoblastomas are rare tumors in young children that can be misclassified as other malignant or benign lipomatous tumors with markedly different outcomes and treatments. We recommend that cytogenetic analysis be routinely used for all pediatric lipomatous tumors to provide an accurate diagnosis and guide appropriate therapy and follow-up.

Paediatric lipoblastoma in the head and neck: three cases and review of literature

Lipoblastoma is a rare benign tumour arising from embryonic white fat. The tumours occur primarily in infancy and early childhood and usually arise from the limbs and the trunk, but neck involvement is rare. We report three cases of head and neck lipoblastoma. In all cases, imaging showed a well-delineated, fat-containing tumour. After surgical resection, the outcome of these patients was uneventful.

Adipose and myxoid tumors of childhood and adolescence

Adipose and myxoid tumors in children are an unusual and challenging group of neoplasms that have some unique aspects in contrast to these tumors in adults. Less than 10% of soft tissue neoplasms in the 1st 2 decades of life have an adipose phenotype and most are benign. The most common are various types of lipoma and lipoblastoma. Liposarcoma in young patients is rare and has a distinctive distribution of histologic subtypes, including classic myxoid liposarcoma, and unusual variants, such as pleomorphic-myxoid liposarcoma. Pathologic examination enhanced by adjunct techniques, such as immunohistochemistry and cytogenetic or molecular genetic studies, is useful for classification of difficult cases. Myxoid tumors can overlap with adipose tumors and are included in this review because of the morphologic similarities and importance of diagnostic accuracy. This article reviews the clinicopathologic features of adipose and myxoid tumors with an emphasis on the unique aspects of these neoplasms in children and adolescents and the differential diagnosis.

Contributions of cytogenetics and molecular cytogenetics to the diagnosis of adipocytic tumors

Over the last 20 years, a number of tumor-specific chromosomal translocations and associated fusion genes have been identified for mesenchymal neoplasms including adipocytic tumors. The addition of molecular cytogenetic techniques, especially fluorescence in situ hybridization (FISH), has further enhanced the sensitivity and accuracy of detecting nonrandom chromosomal translocations and/or other rearrangements in adipocytic tumors. Indeed, most resent molecular cytogenetic analysis has demonstrated a translocation t(11;16)(q13;p13) that produces a C11orf95-MKL2 fusion gene in chondroid lipoma. Additionally, it is well recognized that supernumerary ring and/or giant rod chromosomes are characteristic for atypical lipomatous tumor/well-differentiated liposarcoma and dedifferentiated liposarcoma, and amplification of 12q13–15 involving the MDM2, CDK4, and CPM genes is shown by FISH in these tumors. Moreover, myxoid/round cell liposarcoma is characterized by a translocation t(12;16)(q13;p11) that fuses the DDIT3 and FUS genes. This paper provides an overview of the role of conventional cytogenetics and molecular cytogenetics in the diagnosis of adipocytic tumors.

Mediastinal lipoblastomatosis: report of a case with complex karyotype and review of the literature

Lipoblastoma or lipoblastomatosis is an uncommon fatty tumor seen in children up to the age of 5 years, with very rare exceptions above that age. It usually occurs in the extremities, but it can arise in other anatomical sites, including the head and neck area, trunk, mediastinum, mesentry, and retroperitoneum. We report a 9-month-old boy with mediastinal lipoblastomatosis showing unusually complex chromosomal aberrations. Five years following surgical excision that was incomplete as a result of the tumor's proximity to major blood vessels, the patient developed a recurrence of the tumor in the mediastinum with extension to the neck and spinal dura. We present a review of the literature related to mediastinal lipoblastoma and lipoblastomatosis and the chromosomal abnormalities of these tumors.