β-catenin is a valuable marker for differential diagnosis of osteoblastoma and osteosarcoma.

Osteoblastoma (OB) and osteosarcoma (OS) are 2 bone tumors that predominantly affect young adults. The clinical management of OS differs significantly from that of OB, and thus, accurate diagnosis of OB and OS is critical in determining appropriate treatment modality. However, in certain cases, OS significantly overlaps with OB in clinical and radiographic characteristics, and therefore, the differential diagnosis of OB and OS can be difficult, especially when biopsy material is insufficient. To date, there have been few reports on markers for differential diagnosis of OB and OS. We have previously shown that the Wnt/β-catenin pathway is inactivated in OS. In this study, we aimed to investigate whether the cellular distribution pattern of β-catenin is a potential marker for the differential diagnosis of OB and OS. Immunohistochemical staining was studied in 17 OB samples (21 biopsies; 17 primary and 4 recurrent) and 37 OS samples with complete follow-up information. Moderate-to-strong nuclear β-catenin staining was found in all OB specimens (17/17). In contrast, positive staining of β-catenin was found in the cytoplasm and/or membrane but not the nucleus in all 32 cases of nonchondroblastic OS (32/32) and the classic OS component in chondroblastic OS (5/5). The only positive nuclear β-catenin staining detected in OS biopsies was in chondroblastic OS cells (5/5). In summary, our results indicate that, in addition to conventional histopathologic evaluation, cellular distribution of β-catenin may be used as a valuable marker in the differential diagnosis of OB and OS. Nuclear β-catenin staining strongly suggests OB, whereas cytoplasmic/membranous staining of β-catenin suggests OS.