Japanese Journal of Clinical Oncology 33:482-485 (2003)
© 2003 Foundation for Promotion of Cancer Research
Radiologically and Histologically Mixed Liposarcoma: a Report of Two Biphasic Cases
Departments of 1 Orthopaedic Surgery and 2 Pathology, Tohoku University School of Medicine, Sendai, and 3 Department of Radiology, Iwate Medical University, Morioka, Japan
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONCASE REPORTSDISCUSSIONREFERENCES |
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We report two cases of liposarcomas showing biphasic patterns, radiologically and histologically. The first case was a 52-year-old man with a 17 x 12 cm intramuscular tumor in the right thigh. MR imaging revealed a mass composed of two components: a fat component and another soft tissue component. Histological diagnosis revealed mixed-type liposarcoma consisting of well-differentiated and myxoid liposarcoma. The second case was a 62-year-old man with a 22 x 15 cm intramuscular tumor in the left calf. MR imaging showed a mass composed of fat and non-fat components. The histological diagnosis was well-differentiated and pleomorphic liposarcoma.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONCASE REPORTSDISCUSSIONREFERENCES |
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The World Health Organization (WHO) classifies liposarcomas into four subtypes: well differentiated, myxoid/round, pleomorphic, and dedifferentiated. Liposarcomas rarely have a combined pattern designated as mixed-type liposarcomas (1). Histologically, mixed subtypes in one tumor may be observed occasionally, but cases of more than two distinctive macroscopic tumors existing in one tumor mass have not been well described. We report two cases of unusual liposarcomas showing biphasic patterns, radiologically and histologically.
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CASE REPORTS |
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TOPABSTRACTINTRODUCTIONCASE REPORTSDISCUSSIONREFERENCES |
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Case 1
A 52-year-old man with a tumor in the right thigh was referred to our hospital in December 2001. Physical examination revealed a 17 x 12 cm intramuscular tumor in the posteromedial region of the right thigh. MR imaging clearly revealed that the tumor was composed of two components. The proximal component had high signal intensity (SI) on T1- and T2-weighted images and the distal component had homogenously low SI on T1-weighted images and very high SI on T2-weighted images (Fig. 1). An open biopsy of the mass was performed. The evaluation of the biopsy specimen confirmed the MR imaging findings. The proximal portion was a yellow-tan fat-like mass and the distal portion was myxomatous tissue (Fig. 2). Microscopically, the proximal portion was composed of various-sized fat cells with atypical hyperchromatic nuclei and multivaculolated lipoblasts (Fig. 3a). The distal portion was composed of fusiform cells and bizarre multivacuolated cells in a myxoid matrix with a delicate plexiform capillary vascular network (Fig. 3b). These cells had multiple large and small fat droplets in the cytoplasm. These two components were clearly separated. A diagnosis of the mixed-type liposarcoma consisting of well-differentiated and myxoid liposarcomas was made. The patient underwent radiation therapy because he refused surgery. Unfortunately, the tumor was not responsive to radiation therapy. Lung metastasis developed one year later, and the patient is now under conservative treatment.
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Case 2
A 62-year-old man with a tumor in the left calf visited our outpatient department in October 2001. He observed the mass ten years earlier, and it enlarged progressively during the previous one year. Physical examination revealed a 22 x 15 cm intramuscular tumor in the posteromedial aspect of the left calf. MR imaging showed a tumor composed of two components: a posterior component having high SI on T1- and T2-weighted images, and an anterior component having heterogeneous iso and high SI on T1-weighted image and heterogeneous low and very high SI on T2-weighted image (Fig. 4). Subsequently, a biopsy was performed. The specimen revealed a well-differentiated liposarcoma and high-grade sarcoma. We decided on amputation because the tumor occupied most of the lower leg and inferred that it was impossible to preserve the vessels. Macroscopically, the lesion was composed of a yellow fat-like mass and a firm white mass (Fig. 5). These two foci were clearly separated by a fibrous septa. The microscopic features of the yellow component were various-sized fat cells with atypical hyperchromatic nuclei and multivacuolated lipoblasts, representing well-differentiated liposarcoma (Fig. 6a). Those of the white component were fusiform and polyhedral cells, containing giant bizarre multivacuolated cells, with varying amounts of collagenous stroma (Fig. 6b). These cells had multiple large and small fat droplets in the cytoplasm. A distinctive whorled or storiform pattern was not evident. Immunohistochemically, S-100 positive multivacuolated cells were observed (Fig. 6c). Since pleomorphic lipoblasts were observed, this component was confirmed to be pleomorphic liposarcoma. No sign of recurrence was detected one year after surgery.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONCASE REPORTSDISCUSSIONREFERENCES |
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Liposarcoma is a soft tissue sarcoma that is common in adults; it has a frequency of 16–18% of all soft tissue sarcomas (1–3). According to the 2002 World Health Organization histologic classification of soft tissue tumors, 1iposarcomas can be divided into four categories: well differentiated, dedifferentiated, myxoid, and pleomorphic. However, recent cytogenetic data support liposarcoma classification into three main categories: well differentiated/dedifferentiated, myxoid/round cell, and pleomorphic (4). Approximately 5% of liposarcomas do not fit into the above categories, and they have foci of different histologic features. The WHO designates such tumors as mixed-type liposarcomas. Such liposarcomas that have at least two main subtypes are rare (5).
The tumors in both of our cases had two components: the tumor of case 1 was composed of well-differentiated and myxoid liposarcoma, and the tumor of case 2 was composed of well-differentiated and pleomorphic liposarcoma. The most difficult differential diagnosis was dedifferentiated liposarcoma. According to the WHO classification (2002) the definition of dedifferentiated liposarcoma is "malignant adipocytic neoplasm showing transition from atypical lipomatous tumour/well-differentiated liposarcoma to non-lipogenic sarcoma of variable histological grade." A definitive identification of lipoblasts is a prerequisite for the diagnosis of liposarcoma. Hashimoto (6) and Gebhard (7) recommended the use of the S-100 immunohistochemical stain for separating liposarcomas and malignant fibrous histiocytomas (MFH). In both cases, the high grade part of the sarcoma did not have storiform patterns that are often found in MFH. The myxoid component in case 1 had multivacuolated cells with a delicate plexiform capillary vascular network. These cells contained multiple large and small fat droplets in the cytoplasm. The white component in case 2 showed nuclear pleomorphism and bizarre giant cells with multiple large and small fat droplets in the cytoplasm. These cells were positive in the S-100 immunohistological staining. These histological and immunohistochemical results led to the diagnosis of mixed liposarcoma composed of well-differentiated and myxoid (case 1) and pleomorphic liposarcoma (case 2), rather than dedifferentiated liposarcoma.
Studies based on CT and MR imaging of liposarcomas have been conducted to correlate the macroscopic and histologic features (8–12). Dedifferentiated liposarcoma shows biphasic patterns. However, to the best of our knowledge, there have been no reports on mixed liposarcoma with clearly separated biphasic patterns as in the present cases.
In conclusion, we report 2 cases with biphasic liposarcomas. MR imaging is valuable for demonstrating the biphasic pattern of this type of liposarcoma.
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FOOTNOTES |
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+ For all reprints and correspondence: Taichi Irie, Department of Orthopaedic Surgery, Tohoku University School of Medicine, 1–1 Seiryo-machi, Sendai, Miyagi 980-8547, Japan. E-mail: t-irie{at}gonryo.med.tohoku.ac.jp
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Received April 7, 2003; accepted August 16, 2003
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