Clinical and molecular studies of liposarcoma

Abstract

Aims: (1) To analyse clinicopathological characteristics, treatment and outcome of liposarcoma, and to determine whether, and how, the Scandinavian Sarcoma Group (SSG) treatment guidelines were followed; (2) to analyse tumour volume and morphology response after radiotherapy in myxoid/round cell liposarcoma (MLS/RCLS); (3) to examine the role of the MLS-specific fusion gene FUS-DDIT3 in development of liposarcomas; and (4) to analyse expression patterns of cell cycle regulating proteins in MLS.

Methods: (1) A total of 319 liposarcomas reported between 1986−1998 to the SSG Register were reviewed. Altogether 237 patients without metastasis were analyzed for local recurrences in relation to surgical margins and radiotherapy, metastasis and survival. (2) Thirty-three primary or metastatic MLSs/RCLSs were treated with radiotherapy. Tumour size was measured by MRI or CT. Histopathology was performed of both non-irradiated and irradiated lesions. (3) The fibrosarcoma cell line HT1080 was transfected with the recombinant vectors pFUS-DDIT3-EGFP, pDDIT3-EGFP and pFUSa-EGFP. The tranfectants and the HT1080 cell line were injected into SCID mice, followed by histopathology. The transfected and non-transfected cells were cultured with adipogenic induction medium and microarray-based expression comparison of the different cell lines was performed. (4) Cell cycle controlling factors were analysed by immunohistochemistry and Western blotting in non-irradiated and irradiated MLSs/RCLSs.

Results: (1) Altogether 78% were primarily operated at a sarcoma centre, 45% with wide margins. Only 58% of high-grade (Grades III-IV) lesions with non-wide surgery had postoperative radiotherapy. The risk of local recurrence in this group was 47%, if not irradiated. The estimated 10-year local recurrence-free and metastasis-free survival in the low-grade (Grades I-II) group was 87% and 95% respectively, while in the high-grade group it was 75% and 61%, respectively. Independent adverse prognostic factors for local recurrence were surgery outside a sarcoma centre and dedifferentiated liposarcoma. For metastases, they were old age, large tumour size, high grade and histological type MLS /RCLS. (2) Irradiated MLS/RCLS showed median tumour volume reduction of 52% in 23 tumours. The morphology showed paucicellularity, hyalinization and lipoma-like appearance. There were no obvious differences in volume reduction or morphologic response in MLSs/RCLSs in comparison with MLSs. (3) Cells expressing FUS-DDIT3 and DDIT3 grew in SCID mice as liposarcomas and the capillary network was similar to that found in MLSs/RCLSs. Cells transfected with DDIT3 responded in vitro to adipogenic factors by accumulation of fat, and microarray-based comparison showed that the DDIT3 and FUS-DDIT3 transfected variants shifted toward an MLS/RCLS-like expression pattern. (4) High expression of cyclin D1 and E, their kinases and kinase-inhibitors P16, P27 and P57 was observed, together with low Ki67 and normal cyclin A.

Conclusion: Liposarcoma should be treated at specialized centres and postoperative radiotherapy is indicated for high-grade lesions, at least after non-wide surgery. Low-grade MLSs have high radio-responsiveness, and radiotherapy is indicated after non-wide surgery or in a preoperative setting. The fusion oncogene FUS-DDIT3 and DDIT3 may induce a liposarcoma phenotype, with DDIT3 being the tumour type-determining part of the fusion oncogene. Deregulation of G1-controlling proteins is common and indicates that MLS cells accumulate in late G1 phase.