eP166 - A Rare Case of Dedifferentiated Liposarcoma Presenting as Omental and Mesenteric Sarcomatosis

Purpose/Background: Soft tissue sarcomas (STS) are one of the most common malignancies. Dedifferentiated liposarcoma (DDLPS) is one subtype, and is a rare and aggressive type of connective tissue tumor. Reports of this arising from intraperitoneal sites are rare, with an incidence of 0.1 per 1,000,000 a year.Methods/Interventions: We report of a 54 year-old obese male presenting with a 2-year history of abdominal enlargement with decrease in stool caliber. Physical exam revealed a globular, distended, nontender abdomen. CT scan showed a 28 x 23 x 17.6 cm lobulated mass in the right hemiabdomen, likely involving the omentum (Fig 1AB). He underwent wide excision of the intraabdominal mass with en bloc omentectomy, and resection-anastomosis of segments of ileum and transverse colon for findings of a multilobulated lipomatous mass. Largest was 30 cm and was adherent to segments of the ileum and transverse colon. (Fig 1CD).Results/Outcomes: He was sent home on post op day 10 after experiencing prolonged postoperative ileus. Histopathology showed a multifocal DDLPS with involvement of the ileal serosa, histology grade 3 and was negative for all 8 mesenteric nodes. Immunohistochemistry (IHC) showed positive MDM2, thus, confirming the diagnosis of DDLPS. The multidisciplinary team plan was for the patient to undergo surveillance imaging every 3 months. If found to have metastatic disease, he was to be given Trabectedin, an alkylating agent for unresectable or metastatic STS.Conclusion/

Discussion: Liposarcoma (LS) is a frequent type of tumor and accounts for approximately 10% of all STS’s. They are commonly found in the extremities, retroperitoneum, and gluteal region. One subtype, DDLPS, is uncommon. Primary involvement of the omentum is exceedingly rare. Reports of liposarcoma of the omentum, or mesentery, are only 40, with only 20 DDPLS cases. This population of patients has a mean age of 51 years. The disease carries a five-year disease-specific overall survival rate of 41 to 44%. Lesions in the extremities have better survival rates of 67 to 90%.

Dedifferentiated liposarcoma is a high-grade subtype of STS with a 30% risk of distant metastasis, with predilection to the lungs. They are histologically described as non-lipogenic and may present with amplification of several genes, such as, MDM2, CDK4, HMGA2, and CPM. MDM2 and CDK4 genes are both protooncogenes and the synthesized proteins affect regulation of the cell cycle. MDM2 expression specifically inhibits p53 which also lead to cell proliferation. Often DDLPS presents with decrease in appetite, abdominal distention, and obstructive symptoms. The characteristic imaging appearance of DDLPS is a mass with coexisting fatty and non-fatty tissue. A focal nodular non-lipomatous component >1cm in size is usually found. Calcifications may be observed, denoting a poorer prognosis. No pathognomonic imaging feature can reliably differentiate between the different STS subtypes and definitive diagnosis often require histological analysis.

The recommended approach is complete surgical resection. The standard first line chemotherapy is an anthracycline-based regimen, or it may be combined with an alkylating agent of ifosfamide. Due to its high propensity for local recurrence, radiotherapy may be considered as adjunct to surgery. Although mentioned in literature, there appears to be insufficient evidence supporting the use of hyperthermic intraperitoneal chemotherapy (HIPEC) for peritoneal sarcomatosis. Further studies focusing on novel targeted therapies for MDM2 may be looked into for locally-advanced disease.Dedifferentiated Liposarcoma with omental and mesenteric sarcomatosisCoronal (A) and sagittal (B) CT images showing a lobulated intraabdominal mass (blue arrows) with low attenuation suggestive of fatty tumor. Photographs on exploration (C) and after resection (D) show a multilobulated sarcomatous mass arising from the omentum with extension to the ileum (white arrows) and transverse colon (yellow arrow). Philippine General Hospital, 2023.