Not Your Typical Tumor: A Case of Primary Colonic Liposarcoma

Introduction: A 67-year-old male with a history of follicular cell lymphoma complicated by autoimmune hemolytic anemia underwent computed tomography (CT) of the chest, abdomen, and pelvis for post-treatment surveillance. Case description/methods: The patient had no family history of gastrointestinal malignancy and although he had a personal history of adenomatous polyps, his most recent surveillance colonoscopy was less than one year prior to presentation. CT incidentally identified a 5.5 cm mass at the hepatic flexure and colonoscopy confirmed the presence of a polypoid, glassy-appearing mass in the distal ascending colon, without overlying ulceration, which partially occluded the colonic lumen. Histopathologic evaluation using MDM2 gene amplification by fluorescence in situ hybridization (FISH) identified the mass as a dedifferentiated liposarcoma (DDLS) with intermediate-grade dedifferentiation. The patient underwent right hemicolectomy with resection of regional lymph nodes, all of which were negative for disease. Although the surgically resected margins were positive for well-differentiated liposarcoma, the dedifferentiated portion did not extend to the margins, so no adjuvant chemo- or radiotherapy was recommended. Repeat CT three months later showed no evidence of disease. Discussion: Liposarcoma is a common soft tissue tumor in adults, occurring predominantly in the extremities and retroperitoneum. The colon, however, is a rare site of occurrence with fewer than 20 cases reported historically. Histologically, liposarcomas are identified by the presence of increased MDM2 gene expression and may be categorized into five subtypes: well-differentiated, dedifferentiated, myxoid, pleomorphic, and mixed type. Subtyping is crucial prognostically, as dedifferentiated, round-cell, and pleomorphic liposarcomas exhibit increased local recurrence rates and metastatic potential. Delays in diagnosis may be attributed to typically nonspecific presentations, such as abdominal pain, constipation, and weight loss. Due to the metastatic potential, the recommended treatment of DDLS is complete resection, with post-operative treatment protocols generally following those of retroperitoneal liposarcomas. This case highlights the importance of a high index of suspicion for the rare non-adenomatous colonic lesion with high malignant potential.Figure 1.: Panel 1. Colonic mass, via colonoscope; Panel 2. Colonic mass, following biopsies and distal tattooing; Panel 3. CT of colonic mass (asterisk), with oral and intravenous contrast, axial section; Panel 4. Low power image of interface between colonic mucosa and sarcoma (H&E, 4X).