RESUMO
A dedifferentiated liposarcoma of the retro-peritoneum of a 45-year-old female is described in this case report. It showed dedifferentiation into a histological low-grade type and thus defies the traditional definition of dedifferentiated liposarcoma. The excised specimen was a huge, multi-nodular encapsulated mass surrounding the kidney and infiltrating into it. The mass showed a dedifferentiated focus different in color from the surrounding tumor and containing areas of necrosis and hemorrhage. The sections from the dedifferentiated part of the tumor appeared predominantly as benign spindle cell component on histology but the tumor was infiltrating into the kidney. Hence, a close and long-term follow-up is expected in such cases though they look benign. In the retro-peritoneum, a lipoma-like well-differentiated liposarcoma with spindle cell component, like the present tumor, which shows dedifferentiation, should not be overlooked.