Dedifferentiated Liposarcoma: A Comprehensive Historical Review With Proposed Evidence-based Guidelines Regarding a Diagnosis in Need of Further Clarification

Among all sarcoma types, liposarcoma is the most common sarcoma that develops "dedifferentiation." Since its initial description by Dr Harry Evans, the spectrum of what is now acceptably included under the rubric of "dedifferentiated liposarcoma" (DL) has expanded, sometimes supported by cytogenetic and molecular advances. Similarly, the range of morphologic appearances considered to represent the precursor of DL, atypical lipomatous tumor (ALT)/well-differentiated liposarcoma, also has broadened, not uncommonly creating variants with significant, almost indistinguishable, morphologic overlap with occasional forms of DL, especially problematic in small biopsy specimens. More specifically, the precise criteria separating cellular forms of ALT from what some consider "low-grade" variants of DL remains controversial and inconsistently applied, even among individual pathologists within institutions. For this separation, the only objective and reproducible criteria historically shown to accurately predict a statistically significant difference in prognosis and survival is mitotic rate, alone or incorporated into a histologic grade [eg, Fédération Nationale des Centres de Lutte Contre le Cancer (FNCLCC)], consistently identifying a higher grade neoplasm capable of metastases. While DL may have a better prognosis than other nonmyoid adult pleomorphic soft tissue sarcomas, definitive conclusions are difficult to establish due to nonuniform criteria for staging and establishing tumor size/volume of the high-grade component, compounded by variable definitions and thresholds for rendering the diagnosis of DL. If appropriate therapeutic approaches are to be applied to DL, there needs to uniform agreement regarding the histologic definition, grading, and staging of DL. Herein, is a comprehensive historical perspective on DL and ALT/well-differentiated liposarcoma, seeking to provide insights, updates, and a proposal for uniform, evidence-based guidelines.