RESUMO
BACKGROUND/AIM: Osteoblastoma is a rare benign tumor of the bones in which recurrent rearrangements of FOS have been found. Our aim was to investigate two osteoblastomas for possible genetic aberrations. MATERIALS AND METHODS: Cytogenetic, RNA sequencing, and molecular analyses were performed. RESULTS: A FOS-ANKH transcript was found in the first tumor, whereas a FOS-RUNX2 was detected in the second. Exon 4 of FOS fused with sequences either from intron 1 of ANKH or intron 5 of RUNX2. The fusion events introduced a stop codon and removed sequences involved in the regulation of FOS. CONCLUSION: Rearrangements and fusions of FOS show similarities with those of HMGA2 (a feature of leiomyomas and lipomas) and CSF1 (tenosynovial giant cell tumors). The replacement of a 3'-untranslated region, controlling the gene's expression, by a new sequence is thus a common pathogenetic theme shared by FOS, HMGA2, and CSF1 in many benign connective tissue tumors.