Retroperitoneal liposarcoma with lamellar bone inside

Abstract

In December, 2006, a 65-year-old Japanese man with chronic renal failure was referred to our hospital for the assessment of a large retroperitoneal mass (fi gure A). The mass was resected surgically, and the histopathological diagnosis was an undiff erentiated liposarcoma with areas of osseous metaplasia. 3 years later, a recurrent liposarcoma with bony structures inside (fi gure B) was found in the retoperitoneal space. The resected specimen was viewed by bone histomorphometry after tetracycline double labelling. The bone islands surrounded by adipose tissue showed concentric lamellar structures, with a few osteocytes between the lamella, surrounded by tetracycline double labelling, an osteoid layer, osteoblasts, and fi brous tissue (fi gure C). These fi ndings suggested that osteoid deposit and mineralisation were taking place outwardly. More immature woven bone and cartilaginous tissue were also seen inside the mass. These fi ndings are compatible with the cancer stem cell theory and suggest that our patient’s tumour derived from a mesenchymal stem-like cell that had the potential to diff erentiate into cartilage, bone and adipocytes.