Lipoblastoma mimicking myxoid liposarcoma: a clinical report and literature review.

Lipoblastoma is an uncommon benign lipomatous tumor, occurring typically in children less than 3 years of age. The magnetic resonance image (MRI) is a useful tool for diagnosis of lipoblastoma; its imaging typically shows high-intensity signals on both T1-weighted (T1-W) and T2 weighted (T2-W) images. Here, we present a 12-year-old female patient with a painless mass on the anterior right shoulder. MRI showed the mass with low-intensity signals on T1-W and high-intensity signals on T2-W images. Because of the atypical age and MRI findings, it was difficult to make a conclusive diagnosis of the tumor as lipoblastoma preoperatively. Histopathological examination of the excised tumor showed spindle-shaped or stellate cells embedded in the myxoid matrix, and a few small irregular clusters of mature fat cells that are separated by connective tissue septa. There were some immature, lipoblast-like cells dispersed. These findings are consistent with lipoblastoma, and myxoid liposarcoma was considered as one of the differential diagnosis. We finally diagnosed the tumor as a lipoblastoma for the reasons that there were many mature fat cells and no atypical cells for a myxoid liposarcoma. The postoperative course was uneventful and no recurrence was observed 5 years after the operation. The patient presented is worthy of note due to the unusual characteristics of the tumor. Even in the case of adolescent or older patients with atypical imaging, lipoblastoma should be considered as one of differential diagnosis.

[Ultrastructural analysis of liposarcoma].

9 cases of liposarcoma, including 5 myxoid type, 3 pleomorphic type and 1 well differentiated type, were studied with light, electron microscopy and immunohistochemistry. Comparative observations revealed similarities between liposarcoma cells and cells of developing fat tissue. Liposarcoma cells resemble primary mesenchymal cells, fibroblasts, early, midstage and late lipoblasts or mature lipocytes. But certain differences also exist: First, atypia in liposarcoma cells, such as the appearance of mono- or multinuclei giant lipoblasts in some cases. Second, certain types of liposarcoma are predominated by lipoblasts of a specific stage. Under electron microscope, transitional morphology from both primary mesenchymal cell and fibroblast to lipoblast can be observed, which is an indication that lipoblasts may originate from these two types of cells. Differential diagnosis by electron microscopy is also discussed.

Round cell variant of myxoid liposarcoma in a Japanese Macaque (Macaca fuscata).

A 5-year-old, female, Japanese Macaque (Macaca fuscata) was diagnosed with round cell variant of myxoid liposarcoma. At necropsy, multifocal to coalescing, reddish tan to white nodules, ranging from 0.5 to 1 cm in diameter, were noted throughout the omentum and retroperitoneum. Similar neoplastic nodules were also present in diaphragm, abdominal wall, and on hepatic capsule. Microscopically, neoplastic masses consisted of round to polyhedral cells, which had round, often eccentric nuclei and abundant eosinophilic granular and microvacuolated cytoplasm; Oil red O staining demonstrated large numbers of lipid droplets in the cytoplasm. Ultrastructurally, the cytoplasm of the tumor cells was packed with occasional lipid vacuoles and numerous enlarged mitochondria. Immunohistochemistry revealed tumor cells were positive for vimentin, while negative to cytokeratin, actin, and Factor VIII-related antigen. To the authors' knowledge, this is the first report of round-cell variant of myxoid liposarcoma in nonhuman primate.

The ultrastructure of liposarcomas with attention to "dedifferentiation".

Liposarcomas are among the most common soft tissue sarcomas. It is recognized that dedifferentiation can occur within a well-differentiated liposarcoma, but there is limited information concerning the ultrastructure of the dedifferentiated cells. A series of 8 cases has been studied by light and electron microscopy and compared with well-differentiated, myxoid, and pleomorphic liposarcomas. No definite evidence of lipoblastic differentiation could be found in the dedifferentiated cases. The tumor cells resembled atypical cells in the well-differentiated liposarcomas, supporting the close relationship between these two types of tumors. However, since no conclusive line of differentiation could be found in the dedifferentiated cases, this study supports the contention that these neoplasms are undifferentiated counterparts of well-differentiated liposarcomas.

The myxoid liposarcoma specific TLS-CHOP fusion protein localizes to nuclear structures distinct from PML nuclear bodies.

CHOP in 12q13, also called GADD153 or DDIT3, encodes a transcription factor of the C/EBP type. As a result of t(12;16) translocations, CHOP is rearranged and fused to TLS in 16p11 in about 90% of myxoid liposarcomas/round cell liposarcomas (MLS/RCLS). The TLS-CHOP protein consists of the N-terminal half of TLS juxtaposed to the N-terminal of the entire CHOP. It is capable of forming dimers with the natural dimer partners of CHOP. Here we report that recombinant TLS-CHOP-green fluorescence protein localizes to nuclear structures, similar to, but distinct from, PML nuclear bodies. The TLS-CHOP-green fluorescent protein nuclear structures are resistant to high salt concentration and nuclease treatment. Transfection of TLS-CHOP to normal fibroblasts causes a rapid down regulation and relocation of PML nuclear bodies. An abnormal extra nuclear localization of PML bodies was also found in TLS-CHOP carrying cell lines established from myxoid liposarcomas. Transfection of TLS-CHOP induced a rapid disappearance of PCNA. TLS-CHOP may disturb the nuclear machinery by binding and sequestering important factors from their natural sites.