This report describes an extremely rare case of ascending colonic well-differentiated/dedifferentiated liposarcoma. PubMed was queried for articles published in English from January 1990 to September 2016 with the terms “liposarcoma” and “colon”. Seventy-six articles were returned, of which 13 and 2 described primary colonic well-differentiated and dedifferentiated liposarcoma, respectively. Primary colonic liposarcoma is rare, and only a few cases of dedifferentiated liposarcoma have been reported [3, 4]; therefore, considerations of the characteristics and treatments of primary colonic liposarcoma generally reference those for retroperitoneal tumors.
Dedifferentiated liposarcomas arise from their well-differentiated counterparts and thus exhibit cytogenetic similarities. Immunohistochemistry for CDK4, MDM2, and p16 expression aids in the differential diagnosis of well-differentiated and dedifferentiated liposarcoma from other adipocytic neoplasms . Despite this, the two display significantly different biologic behaviors. Low-grade, well-differentiated tumors can recur as high-grade, dedifferentiated disease characterized by increased local recurrence rates and metastatic potential. For instance, retroperitoneal well-differentiated and dedifferentiated liposarcomas were associated with 3-year local recurrence rates of 31% and 83%, respectively. Approximately 20–30% of dedifferentiated liposarcomas result in distant recurrence, as opposed to only 3% of well-differentiated tumors—of which all belonged to the sclerosing subtype. Moreover, dedifferentiated liposarcoma is associated with a 4–6-fold increased risk of death when compared with well-differentiated cases [6, 7].
In this case, the dedifferentiated liposarcoma formed a firm mass that was easily identified; however, the well-differentiated sections were soft and difficult to distinguish from the fat tissue surrounding the ascending colon during the operation. We therefore recommend that when dedifferentiated liposarcomas are resected, an adequate margin of soft fatty tissue around the solid tumor also be resected to ensure that no well-differentiated liposarcoma remains. Given that it is difficult to diagnose dedifferentiated liposarcoma preoperatively, submucosal tumors suspected of being high-grade sarcomas need to be resected with adequate margins that include soft tissue around the firm tumor.
Positive margins increase the risk of local recurrence, their influence on overall survival is less clear. Positive microscopic margins (R1) are reportedly associated with higher distant recurrence rates and poorer prognoses than negative microscopic margins (R0) , but other studies have failed to demonstrate this relationship [6, 9]. Moreover, 72% of patients with positive margins had no recurrence . Positive margins were poor prognosis than negative margins in the high-grade tumor; however, surgical margins were not related with prognosis in the low-grade tumor .
Postoperative treatment for liposarcoma remains controversial. Adjuvant radiotherapy limits the risk of local recurrence, but no definite survival benefit has been established  and patients often experience severe adverse effects attributed to cell death in the surrounding normal tissues—primarily the small bowel . In 1054 patients undergoing resection of primary retroperitoneal sarcoma, 276 patients underwent radiotherapy. But the radiotherapy had no significant impact on prognosis (HR, 0.95; 95% CI, 0.78–1.15; P = 0.6) . Recent study reported the survival benefits of adjuvant radiotherapy, but the postoperative radiotherapy effect does not depend on surgical margin status (HR 0·93; 95% CI 0·79–1·10; P = 0.38) . Comparatively, adjuvant chemotherapy with a doxorubicin-based regimen ((EORTC 62771: doxorubicin, dacarbazine, cyclophosphamide and vincristine; EORTC 62931: doxorubicin and ifosfamide) is an independent favorable prognostic factor for relapse-free, but not overall, survival [14, 15]. In this case, low-grade, well-differentiated liposarcoma were positive but dedifferentiated liposarcoma was completely resected, and no adjuvant therapy was given based on previous studies.
The following recommendations for evaluation during follow-up of retroperitoneal sarcoma have been published by the Trans-Atlantic RPS Working Group. Because the median time to recurrence of high-grade retroperitoneal sarcoma is less than 5 years after definitive treatment, the intervals between follow-up evaluations should be 3 to 6 months for 5 years. After 5 years, annual follow-up is considered adequate. After incomplete resection of retroperitoneal sarcoma patients should be followed indefinitely because the risk of recurrence does not plateau .