Case 98

A 54 year old female with a perirenal mass.

1.What's your diagnosis?

A: Well differentiated liposarcoma

B: Dedifferentiated liposarcoma

C: Pleomorphic liposarcoma

D: Reactive fibroblast favor nodular fasciitis

E: Low grade dedifferentiated liposarcoma

Answer

This is a case of well differentiated liposarcoma. If you don't see the lipogenic area, a dedifferentiated liposarcoma is still not favored due to the low mitotic count.

• Lack of Consensus on DDLPS Criteria:

  • Histologic criteria for DDLPS remain controversial; various definitions are used across studies.

• Diverse Diagnostic Approaches:

  • Only one group strictly followed Evans’ criterion (≥5 mitoses/10 HPFs) before applying FNCLCC grading.

  • Other studies used:

    • Purely descriptive criteria.

    • Descriptive criteria with modifications to FNCLCC grading.

    • Descriptive approaches without requiring a specific mitotic count.

• Variability in Defining Low-Grade DDLPS:

  • Some studies use descriptive terms like “low-grade dedifferentiated” or compare with cellular WDLPS.

  • Diagnostic ambiguity affects understanding of the biological behavior and clinical relevance of “low-grade” DDLPS.

• FNCLCC Grading System Constraints:

  • Once a tumor is labeled DDLPS (given differentiation score 3), its minimum FNCLCC grade is 2.

  • Even with low mitotic activity (e.g., 0–1 mitoses/10 HPFs) and no necrosis, the grade cannot be <2.

  • WDLPS with similar features would be graded as FNCLCC grade 1 due to a lower differentiation score.

• Diagnostic Inconsistency Risks:

  • Inconsistent criteria lead to nonuniform DDLPS classification, affecting treatment and prognosis evaluations.

• Evans’ 1979 Mitotic Criterion:

  • The only objective and reproducible criterion: ≥5 mitoses/10 HPFs + presence of NLA (nonlipogenic areas).

  • Evans also showed prognostic differences using this threshold, separating WDLPS from true DDLPS.

• Implications for Grading and Prognosis:

  • Tumors with <5 mitoses/10 HPFs may behave like WDLPS.

  • Suggests these should not be called DDLPS or graded using FNCLCC unless they meet mitotic threshold.

Reference: Does “Low-Grade” Dedifferentiated Liposarcoma Exist? The Role of Mitotic Index in Separating Dedifferentiated Liposarcoma From Cellular Well-differentiated Liposarcoma The American Journal of Surgical Pathology 47(6):p 649-660, June 2023. | DOI: 10.1097/PAS.0000000000002037

Case credit: UCSD Pathology

Author: Wangpan Jackson, Shi, MD