Myxoid liposarcoma: a well-defined clinical target variant in radiotherapy for soft tissue sarcoma.

tissues that show even more diverse characteristics than those originating from epithelial tissues [1]. Despite the diverse histological types of STS, these are generally managed and researched as uniform diseases due to their rarity, except for several unique histologic subtypes [2,3]. Nevertheless, the distinct characteristics, variety of treatment responses, and differences in oncologic outcomes between the subtypes of STS, strongly suggest the need for patientand/or subtype-specific customized treatment approaches [1]. The efficacy of radiotherapy (RT) in resectable STS on reducing local recurrence has been quite clearly confirmed in meta-analysis [4]. Additionally, preoperative RT was significantly more advantageous than postoperative RT in terms of local control rate either in retroperitoneal sarcomas or sarcomas of other sites. This beneficial effect on the local control of preoperative RT in STS is highlighted even more in view of its’ lower radiation dose, small target volume, and reducing long-term toxicities, including fibrosis, edema, and joint stiffness. Furthermore, preoperative RT may prevent tumor seeding during surgical management, and thicken and eliminate or minimize viable tumor cells in the pseudocapsule, which can be used as a reference for resection to achieve wider surgical margins [5]. Despite the proven advantages of preoperative RT in STS, the objective response rate is quite limited, at approximately 25% (range, 0% to 50%) in actual clinical practice, except for myxoid liposarcoma (MLS) [6]. Considering that definite surgical resection is planned and unnecessary resection of the surrounding normal organs should be minimized, it is clear that the change in tumor volume itself is also one of the crucial outcomes that cannot be ignored in the management of STS [7]. The importance of tumor volume response could be particularly emphasized for locally advanced unresectable sarcomas [8]. MLS is one of the five types of liposarcomas according to the 2020 World Health Organization classification [1]. MLS is clearly distinguished from the other subtypes of liposarcoma by the presence of the pathognomonic fusion gene FUS-DDIT3 (also known as TLS-CHOP) or less often, as much as 10%, ESWR1-DDIT3 [9], although the variability of the fusion gene transcript is not associated with clinical outcome [10]. MLS also shows unique clinical features, like occur more younger age, and mostly in the thigh rather than the retroperitoneum, and metastasize to sites other than the lungs, including soft tissue or bone [11]. The most notable difference is that, unlike other subtypes of sarcoma, including other types of liposarcomas, which are generally considered resistant to radiotherapy, MLS is much more sensitive to RT. One explanation for the higher RT responsiveness of MLS Myxoid liposarcoma: a well-defined clinical target variant in radiotherapy for soft tissue sarcoma