β-Catenin accumulation and gene mutation in exon 3 in dedifferentiated liposarcoma and malignant fibrous histiocytoma

Context.- β-Catenin is an adhesion molecule that also plays a role in the Wnt signaling pathway. Objective.- To analyze β-catenin mutation and accumulation in a series of liposarcomas and malignant fibrous histiocytomas. Design.- β-Catenin mutation in exon 3 was studied using polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) and direct sequencing analysis in 30 formalin-fixed, paraffin-embedded liposarcomas. The tumors included 12 dedifferentiated liposarcomas, characterized by both high-grade anaplastic components and well-differentiated liposarcoma components, plus 18 well-differentiated liposarcomas (10 lipoma-like and 8 sclerosing-type cases). The 2 components of dedifferentiated liposarcomas were analyzed independently. β-Catenin accumulation in the nuclei or cytoplasm and Ki-67 expression (cell-proliferation marker, MIB-1 labeling index) were examined immunohistochemically. Nine storiform-pleomorphic-type malignant fibrous histiocytomas were also studied. Results.- Dedifferentiated liposarcomas showed mutation in 2 cases (17%) and accumulation in 5 cases (42%). One of the 2 cases that showed mutations had a mutation in the well-differentiated component; this mutation was silent. The other case had mutations that differed between the 2 components. In well-differentiated liposarcomas, mutation was not seen in any of the cases (0/18; 0%); however, accumulation was seen frequently in the sclerosing-type cases (5/8; 63%), but not in the lipoma-like cases (0/10; 0%). Malignant fibrous histiocytomas showed mutation and accumulation in 5 (56%) and 4 (44%) cases, respectively, without any exact correlation between the cases. Cases with accumulation had a higher MIB-1 labeling index than those without, among both the sclerosing-type well-differentiated liposarcomas (P < .05) and the malignant fibrous histiocytomas. Conclusions.- Our results suggest the possible involvement of β-catenin activation caused by β-catenin mutation in liposarcoma and malignant fibrous histiocytoma, but the contribution would seem to be different, depending on the tumor type. β-Catenin accumulation is also thought to be related to cell proliferation in some of the cases.