A case of dedifferentiated liposarcoma with well-differentiated liposarcomatous, inflammatory myofibroblastic tumor-like, and low- and high-grade osteosarcomatous components: common MDM2 amplification supporting divergent morphological change of well-differentiated liposarcoma

Myofibroblastic dedifferentiation of well-differentiated liposarcoma (WDL) has rarely been documented, and WDL-associated low-grade osteosarcoma (OS) is extremely rare. Here we present a case of a 51-year-old man with three adjacent retroperitoneal masses corresponding to WDL, inflammatory myofibroblastic tumor (IMT)-like, and lowand high-grade OS components. Regarding the IMT-like and low-grade OS components adjacent to the WDL component, it was ambiguous whether they represented WDL dedifferentiation or were primary tumors. In our case, all of the abovementioned components exhibited MDM2 amplification. Even though MDM2 amplification could be observed in primary IMT and primary low-grade OS, this finding strongly supported that those components constituted the spectrum of a single tumor along with their spatial relationship.