Case #14

Typical Clinical Presentation:
A 56-year-old female presented with a rapidly growing, large, destructive lesion in the pelvic bones.
Characteristic Radiological Findings:
  • CT scan of the pelvis shows a destructive bone lesion, which extends through the cortex into the soft tissues.
Pathological Findings: :
  • Microscopic examination reveals a distinguishing feature of this entity. That is the presence of two distinct components: a low-grade cartilaginous neoplasm and a high-grade sarcoma.
  • High-grade component has the morphology of MFH. Numerous mitoses including atypical mitoses are present.
  • The cartilaginous component is a low-grade chondrosarcoma (Grades 1 to 2).

Diagnosis: Dedifferentiated Chondrosarcoma

Salient Points::
  • Dedifferentiation means transformation of a low-grade (grades 1 or 2) chondrosarcoma into a high-grade sarcoma, most often with features of MFH or osteosarcoma. By definition, the hallmark of dedifferentiated neoplasm is the co-existence of two components, a low-grade lesion and a high-grade sarcoma, with abrupt demarcation between them. This feature distinguishes dedifferentiation from a gradual increase in grade. Clinically, dedifferentiation is heralded by a sudden increase in aggressiveness (eg., development of a rapidly growing soft tissue mass).
  • Most patients are older than 50 years.
  • Prognosis. This variant of chondrosarcoma is associated with a very low survival rate. The response to treatment is poor and widespread metastases are the rule.
  • Experimental data: Controversy remains as to whether both components of dedifferentiated chondrosarcoma are derived from a common precursor cell or they represent two separate lineages (collision tumor). The current hypothesis is that "high-grade components represent a failure of differentiation, rather than de-differentiation of mature chondroid cells". In a recent study by Bovee et al, molecular genetic characterization of both components of a dedifferentiated chondrosarcoma has provided evidence for a monoclonal origin and has suggested that the separation may be an early event in the histogenesis of this tumor.
Available publications for the topic:  Dedifferentiated Chondrosarcoma

Selected References::
  1. Bovee JVMG, Cleton-Jansen AM, Rosenberg C, Taminiau AHM, et al. Molecular genetic characterization of both components of a dedifferentated chondrosarcoma, with implications for its histogenesis. J Pathol 1999;189:454-462