From the archives of the AFIP: imaging of musculoskeletal liposarcoma with radiologic-pathologic correlation

Liposarcoma is the second most common type of soft-tissue sarcoma, accounting for 10%-35% of these lesions. The World Health Organization has categorized soft-tissue liposarcomas into five distinct histologic subtypes: well differentiated, dedifferentiated, myxoid, pleomorphic, and mixed type. Well-differentiated liposarcomas frequently demonstrate a diagnostic appearance on computed tomographic (CT) or magnetic resonance (MR) images, with a largely lipomatous mass (>75% of the lesion) and nonlipomatous components in thick septa or focal nodules. The CT or MR imaging finding of a nodular dominant focus (>1 cm in size) of nonlipomatous tissue in a well-differentiated liposarcoma suggests dedifferentiated liposarcoma, and biopsy should be directed at the nonadipose component. The high water content of myxoid liposarcoma seen at pathologic analysis and constituting the majority of the lesion is reflected at sonography, CT, and MR imaging. However, the detection of a small amount of adipose tissue in the septa or as small nodular foci superimposed on the background of myxoid tissue allows prospective diagnosis in 78%-95% of myxoid liposarcomas. Pleomorphic liposarcomas are high-grade sarcomatous lesions and typically appear as heterogeneous soft-tissue masses, although small amounts of fat are seen on MR images in 62%-75% of cases, findings that suggest the diagnosis. Mixed-type liposarcomas have features representing a combination of the other subtypes. Primary liposarcoma of bone is exceedingly rare and usually demonstrates aggressive nonspecific features, although fat may be seen. Understanding and recognition of the spectrum of appearances of the various types of musculoskeletal liposarcoma, which reflect their underlying pathologic characteristics, improves radiologic assessment and is vital for optimal patient management.

COL1A1-PDGFB fusion transcripts in fibrosarcomatous areas of six dermatofibrosarcomas protuberans

The fibrosarcomatous transformation of dermatofibrosarcoma protuberans (DFSP) has been considered for some time to be associated with an adverse clinical outcome. However, the molecular and cellular mechanism underlying the tumor progression remains undetermined. As the chimeric gene, COL1A1-PDGFB, has been proposed to play an important role in the histogenesis of DFSP, we conducted a reverse transcription-polymerase chain reaction assay to ascertain whether the COL1A1-PDGFB fusion transcripts can be detected in both conventional DFSP and fibrosarcomatous components of DFSP with fibrosarcomatous areas (DFSP-FS), using a simple method of microdissection on sections of archival formalin-fixed, paraffin-embedded tumor specimens from six DFSP-FS cases. The COL1A1-PDGFB fusion transcripts could be detected in FS areas in five of the six cases, whereas conventional DFSP areas of all cases expressed the chimeric mRNA. A subsequent sequence analysis of the polymerase chain reaction products confirmed that the detected messages were derived from identical gene fusions in the two different components of each of the five cases. Our results verify that the COL1A1-PDGFB fusion transcripts are preserved in the FS areas of most DFSP-FSs. The expression of the fusion transcripts in both conventional DFSP and FS areas of DFSP-FS supports a common histogenesis of the two components.

Retroperitoneal liposarcoma with combined well-differentiated and myxoid malignant fibrous histiocytoma-like myxoid areas

To broaden the knowledge of myxoid morphology in liposarcoma, eight cases of unusual liposarcoma with combined well-differentiated and myxoid malignant fibrous histiocytoma (MFH)-like myxoid areas are reported. The tumors arose as huge retroperitoneal masses in elderly patients, except for one that occurred in the spermatic cord. Three cases had local recurrences, and one of the seven patients who were followed up had died of the tumor. Grossly, the tumors were mostly confluent and multinodular and showed a glistening myxoid appearance in variable proportions, which merged gradually into or were juxtaposed to yellow fatty or sclerotic whitish areas. Microscopically, in addition to areas of well-differentiated lipoma-like or sclerosing liposarcoma, all the tumors contained myxoid portions characterized by scattered multinucleated or bizarre giant cells and a prominent plexiform vascular pattern that resembled myxoid MFH or myxofibrosarcoma. The myxoid areas were associated with discernible lipogenesis. High-grade dedifferentiation was present in one tumor. Cytogenetically, in one case, the myxoid lesion had nonrandom chromosomal aberrations, such as ring and marker chromosomes, characteristic of a well-differentiated variant of liposarcoma. In a nested reverse transcription-polymerase chain reaction analysis using archival paraffin-embedded tissue, it was seen that none of the eight tumors with myxoid MFH-like features had TLS/FUS-CHOP fusion transcripts characteristic of myxoid and round cell liposarcomas. These clinicopathologic and molecular features suggest that the current myxoid tumors are more closely related to well-differentiated liposarcoma rather than to ordinary myxoid liposarcoma despite their unequivocal myxoid morphology. Missense point mutations of the p53 gene were detected in two (25%) cases by single-strand conformation polymorphism and sequence analyses. Immunohistochemical expressions of p53 and mdm2 were observed in 75% of the cases, in which immunoreactive tumor cells were seen more often in the myxoid MFH-like areas. Thus, altered p53 pathways, such as p53 gene mutation and mdm2-mediated inactivation of p53, may play a pathogenetic role in this form of tumor progression showing myxoid MFH-like morphology in liposarcoma, as has been suggested in dedifferentiated liposarcoma.

Liposarcoma with meningothelial-like whorls: a study of 17 cases of a distinctive histological pattern associated with dedifferentiated liposarcoma

AIMS

We reviewed 17 cases of liposarcoma with peculiar meningothelial-like whorls to determine the pathological and clinical significance of this distinctive morphological finding.

METHODS AND RESULTS

Seventeen liposarcomas with concentric whorls simulating the whorls seen in meningioma, were retrieved from the soft tissue registry of the Armed Forces Institute of Pathology. There were 10 males and seven females with a mean age of 53 years (range 24-76 years). Twelve of the 17 cases were large retroperitoneal tumours (mean 170 mm in greatest dimensions). All 17 cases had whorls. Three cases were classified as well-differentiated liposarcoma with whorls and bone formation. Five cases showed coalescing of whorls into areas which may be interpreted as low to intermediate grade dedifferentiation. Five cases had spindled areas associated with the whorls which correlate with classical intermediate to high-grade dedifferentiation. Finally, four cases had a predominant spindle cell component resembling malignant fibrous histiocytoma with focal residual possible sclerosing well-differentiated liposarcoma (scattered adipocytes, adipocytic atypia and/or floret-type giant cells). The meningothelial-like whorls were clustered or scattered throughout the tumours and ranged from 0.09 mm to over 10 mm in diameter in cases with coalescent whorls. Metaplastic bone was present within the whorls or in their immediate vicinity in 10 of 17 cases. Immunohistochemically, the whorl-forming spindle cells showed alpha-smooth muscle actin reactivity in three of seven cases but were negative for epithelial membrane antigen, CD21, and CD35 indicating lack of relationship with meningioma and dendritic reticulum cell sarcoma, other tumours that may contain whorls. Whorls with bone formation revealed cells adjacent to the bone to be positive for osteocalcin, a marker of osteoblastic phenotype. The spindle cells of the whorls were negative for CD34 and CD31, yet these highlighted numerous capillaries inside the whorls in a concentric manner. The whorl-forming cells showed moderate to high MIB-1-index and showed p53 immunoreactivity similar to the dedifferentiated areas but differed from the areas of well-differentiated liposarcoma, which were p53-negative and showed a low MIB-1-index. Follow-up (available in 65% cases) revealed seven patients with metastases or dead of the disease and five patients with one or more recurrences.

CONCLUSIONS

The meningothelial-like whorls represent a mesenchymal proliferation which may undergo pericytic or myofibroblastic, or occasionally osteoblastic, differentiation in liposarcoma. These whorls do not represent dendritic or perineurial/meningothelial differentiation. The significant proliferative activity, p53 reactivity and tendency to coalesce and associate with dedifferentiated liposarcoma suggest that the meningothelial whorls may represent an early sign of dedifferentiation of liposarcoma.

Dedifferentiated liposarcoma: a clinicopathological analysis of 155 cases with a proposal for an expanded definition of dedifferentiation

We studied 155 cases of dedifferentiated liposarcoma to define its clinicopathologic features and behavior, in particular how the extent and grade of dedifferentiation affected outcome. Tumors occurred in late adult life (median, 61.5 years: range, 21-92 years), most commonly in the retroperitoneum (106 cases), extremities and trunk (32 cases), and scrotum/spermatic cord (13 cases). The majority of dedifferentiated liposarcomas presented as de novo lesions, whereas the remainder developed as a late complication of a preexisting well-differentiated liposarcoma after an average interval of 7.7 years. At the time of presentation, most of the dedifferentiated liposarcomas displayed extensive areas of high-grade dedifferentiation resembling malignant fibrous histiocytoma or high-grade fibrosarcoma, whereas a minority contained only areas of low-grade dedifferentiation resembling fibromatosis or well-differentiated fibrosarcoma. Divergent myosarcomatous or osteosarcomatous differentiation was observed focally in six cases. The behavior of dedifferentiated liposarcomas was that of a high-grade sarcoma with a local recurrence rate of 41%, a metastatic rate of 17%, and disease-related mortality of 28%. The most important prognostic factor was location in that retroperitoneal tumors had significantly worse survival than those in other sites. Tumors were divided into those having less than or those with more than 25% dedifferentiation, and dedifferentiated zones were classified into low grade or high grade. Neither low-grade dedifferentiation nor a low percentage of dedifferentiation was associated with an improved outcome for the tumors examined in this study; however, in no cases was the absolute size of the dedifferentiated focus <2 cm. Therefore, this study did not determine a minimum, or threshold, amount of dedifferentiation below which outcome was more favorable. The behavior of liposarcomas in which the dedifferentiated component was entirely low grade was more similar to that of traditional dedifferentiated liposarcoma than to that of well-dedifferentiated liposarcoma. Our study supports the expansion of the definition of dedifferentiated liposarcoma to include tumors with low-grade dedifferentiation and also suggests that low-grade dedifferentiation represents a precursor lesion of high-grade dedifferentiation.

Molecular abnormalities of the p53 pathway in dedifferentiated liposarcoma

Dedifferentiated liposarcoma represents a distinct subtype of liposarcoma and is characterized by the presence of abrupt transition from well-differentiated liposarcoma to high-grade pleomorphic sarcoma (mostly MFH-like). A key role for p53 in tumour progression of this subset of liposarcomas has been suggested on the basis of p53 immunopositivity. A series of 14 dedifferentiated liposarcomas has been investigated by analysing the p53 gene and protein together with the p53-related molecules p21Waf1 and mdm2, to verify whether the p53 pathway is involved in the development and progression of this tumour type. The results indicate that the p53 gene is rarely involved in dedifferentiated liposarcoma (7 per cent of cases analysed) and that low percentages of p53 immunopositivity are still compatible with integrity of the p53 gene. This concept is also supported by the observed preservation of p21Waf1 immunoreactivity in all but the p53-mutated cases. By contrast, mdm2 overexpression emerges as the most frequent abnormality in dedifferentiated liposarcoma (57 and 78 per cent of cases in well-differentiated and high-grade areas, respectively).