Ronald S. A. de Vreeze, Frits van Coevorden, Lucie Boerrigter, Petra M. Nederlof, Rick L. Haas, Johannes Bras, Andreas Rosenwald, Thomas Mentzel, Daphne de Jong

• Aims Chondroid lipoma (CL) is a benign tumor that mimics a variety of soft tissue tumors and is characterized by translocation (11;16). Here, we analyze CL and its histological mimics. Methods CL ( ) was compared to a variety of histological mimics ( ) for morphological aspects and immunohistochemical features including cyclinD1(CCND1). Using FISH analysis, CCND1 and FUS were investigated as potential translocation partners. Results All CLs were strongly positive for CCND1. One of 4 myoepitheliomas, CCND1, was positive. InAims Chondroid lipoma (CL) is a benign tumor that mimics a variety of soft tissue tumors and is characterized by translocation (11;16). Here, we analyze CL and its histological mimics. Methods CL ( ) was compared to a variety of histological mimics ( ) for morphological aspects and immunohistochemical features including cyclinD1(CCND1). Using FISH analysis, CCND1 and FUS were investigated as potential translocation partners. Results All CLs were strongly positive for CCND1. One of 4 myoepitheliomas, CCND1, was positive. In well-differentiated lipomatous tumors and in chondrosarcomas, CCND1 was frequently expressed, but all myxoid liposarcomas were negative. FISH analysis did not give support for direct involvement of CCND1 and FUS as translocation partners. Conclusions Chondroid lipoma is extremely rare and has several and more prevalent histological mimics. The differential diagnosis of chondroid lipomas can be unraveled using immunohistochemical and molecular support.…