Retroperitoneal liposarcoma with colonic involvement: a case report.

A 72-year-old male visited a local hospital on presentation of melena. Colonoscopy revealed a protruded lesion in the ascending colon, and computed tomography revealed a 20 cm retroperitoneal tumor. Biopsy failed to provide a definitive diagnosis of the colonic lesion. He was diagnosed as having a retroperitoneal liposarcoma and an ascending colon tumor using computed tomography, and referred to our hospital. Biopsy of the ascending colon lesion showed spindle cells with fibrosis. On immunohistochemical staining, tumor cells were positive for cyclin-dependent kinase 4 and murine double minute 2, and the lesion was diagnosed as a well-differentiated or dedifferentiated liposarcoma. The retroperitoneal liposarcoma, which had infiltrated the ascending colon, was resected along with the right colon and the right kidney. Macroscopically, the tumor had infiltrated the ascending colon, forming a multinodular solid mass in the lumen and the right kidney. Microscopic finding of the main tumor revealed a well-differentiated liposarcoma, and that of the colonic lesion revealed a dedifferentiated liposarcoma with nuclei of different sizes and shapes and increased spindle cell morphology. The right kidney and ureter were surrounded by tumor cells but were not infiltrated, and there was no lymph node involvement. The diagnosis of retroperitoneal liposarcoma is often difficult because symptoms appear only after the tumor becomes very large. Some retroperitoneal liposarcomas are found on computed tomography by chance. The clinical course of this case was very rare because of the presentation of melena as the first symptom and the detection of an invasive mass in the ascending colon using colonoscopy.