Dedifferentiated Giant Cell Tumour of Bone in the Form of Low-Grade Fibroblastic Osteogenic Sarcoma: Case Report of a Unique Presentation with Follow-Up

A Nahal,A Ajlan,T Alcindor,R Turcotte

doi:10.3747/co.v17i4.571

Abstract

Giant cell tumour (GCT) of bone is a locally aggressive benign tumour. It can, however, undergo dedifferentiation, either de novo or secondarily after local recurrence or radiation. Whether spontaneously occurring or induced by previous irradiation, this malignant transformation is typically defined as a high-grade anaplastic sarcoma devoid of giant cells. Dedifferentiation of GCT into low-grade-appearing sarcoma has not been reported yet. Here, we describe the first case of dedifferentiated GCT in the appearance of low-grade fibroblastic osteogenic sarcoma with distant bone metastases. This disease progression occurred without previous irradiation. We confirm the aggressive behaviour of this tumour despite the deceptively bland appearance of the malignant component. We also alert others to the importance of recognizing this rare histology to avoid underdiagnosis and subsequent undertreatment.

Highlights

Malignant transformation of giant cell tumour of bone, known as dedifferentiation of gct, is a rare event that occurs in fewer than 1% of all cases 1
We report a unique case of gct in which dedifferentiation occurred in the form of low-grade fibroblastic osteogenic sarcoma without prior radiation
Malignancy arising in gct of bone is histologically suspected when a high-grade sarcoma is observed either in close contact with a typical gct or in a patient with a known history of gct [2,3]

Summary

INTRODUCTION

Malignant transformation of giant cell tumour (gct) of bone, known as dedifferentiation of gct, is a rare event that occurs in fewer than 1% of all cases 1. Most secondary cases are characterized by a history of previous irradiation; spontaneous malignant transformation is exceedingly rare [4,5]. Occurrence of malignancy is important to diagnose, because it entails a worse clinical outcome, including more aggressive local behaviour and a higher risk for metastatic disease 6. The diagnosis is established by histology, it is suspected both clinically and radiographically. Despite the bland appearance of the dedifferentiated component, local recurrence and metastases to distant bone occurred, indicating aggressive behaviour. We alert others to the importance of recognizing such rare histology to avoid inadequate management

CASE DESCRIPTION

Findings

DISCUSSION

CONCLUSIONS